Grandson is a nightmare to look after

I would refuse to let him sleepover whilst he is like this-or be visiting without a parent. Speak to his parents and tell them you wont have this behaviour, simple as that.Maybe he does/doesnt have an underlying reason for misbehaving but its up to the parents to discover what, but you should not have to go through this.

BlueBelle

*He’s the only one I genuinely struggle with, and I’m finding it really hard to even warm to him*

….and he knows it, he knows you don’t like him that much, he knows you prefer his sister, he hasn’t at 6 got the verbal intelligence to sit down and say ‘ nan why don’t you like me’ so he does what many 6 year old would do he looks for attention, any attention he looks to disrupt and yes to give you a hard time as he feels you’re giving him a hard time
He’s good at school, he gets on with his grandad, so I d be surprised if he’s anything other than a little boy trying to punish you for not liking him
Change it around, play with him, have a giggle with him, kick a ball round, play a board game, draw with him, read an exciting story to him, find your route into him and most of all tell him you love him
I d have the children separately for a little while that way he’s not having to share anything you can give him your undivided attention which is what is begging for , he played his music louder and louder so you would know he was there a telling off is better than silence

I’m not blaming you just hopefully encouraging you to look at it through his eyes

BlueBelle, IMHO I think you've summed the situation up perfectly! Sounds to me like an attention seek.

I agree with bluebelle

Talk to the parents who are RESPONSIBLE for him, especially if he kicks off at home. It could be something as simple as a reaction to some foods. Don't tolerate such behaviour, why should you?
I know you may feel you should be able to care for him, but not as he is. He is not gaining anything from visits to you if he screams etc all the time. Why should you put up with this.? If he is good at school then he can be good with you.
If this was your child what would you do? I suspect you would sort this out one way of another. Unless his behaviour is looked into now, find a reason and make steps to alter it he will not learn how to behave anywhere.
Sorry if this is hurtful, you are the grandparents and having your grandchildren should be fun without the screaming. Do not the parents worry? Can you investigate with the parents why does he not want to come to you and why do they send him?

Just a quick add on. Our grandson who is now 26 and a wonderful young man used to come here, however he never wanted to stay overnight with us! We tried to settle him, no screaming etc, but we understood and took him back home where he slept well and would come round all day.
We have a wonderful relationship, visits us when he is near. We never pushed it and in the end we arranged for him to be collected or taken home near bedtime.
Our daughter understood the problem and we worked with it. Well it wasn't a problem we worked around it.

Talk to the parents. He's clearly out of control. Don't have him until he learns how to behave.

“His sister said he doesn’t like you because you’re mean” this is from the 8 year old you get on with. Strange that she should say this if all you’re doing is asking him to say please or thank you,
Firstly he’s 6. That’s young and still learning. Odds are he’s sussed out you’re not so keen on him and is hurt or angry. Refusing to have him over or making more fuss of his sister is unlikely to improve your relationship.
Wouldn’t the best thing be to get his mum and dad to talk to him to find out why he has a thing about you. Maybe you are doing something that upsets him that you’re not aware of.

“He’s clearly out of control” …..he’s 6. As others have said he could have ADHD or some form of autism or just be a typical boy. Why condem him without finding out what’s really going on.

I wonder if he wanted to stay over or he was given no choice at all, making the whole scenario worse

Tell his parents to bring him back when he is better behaved.
Meantime get a rescue dog or cat, enjoy life and always be too busy to look after him!

You say that you would have your GD any time, I know it sounds really harsh, but I would tell him that if he doesn't behave himself, then next time there's an opportunity to come and stay, you'll only be having his sister. He may think he doesn't like you, but if you discuss it with his parents, and ask them not to spoil him while his sister is away, then you might find that he decides your rules aren't so bad after all, and realise that he's missing out. With my own granddaughters, (I have 3 of them), like you, I had my own rules, but I was lucky, in as much as they lived close by, so I saw them frequently as little ones, and they grew up knowing that Nana's house, meant Nana's rules, and because I made their visits enjoyable as long as they stuck to the rules, they loved coming to visit. Sorry I haven't read the full thread, so you may have already mentioned it, but is it possible that you don't see your grandchildren often enough for them to enjoy their visits in spite of your rules?

Op

Do you expect your 6 year old gs to say thank you and please - how often? All the time?

If you take the advice of " i will only babysit your sister till you learn to behave", he may hate you more for a good reason

This sounds to me like attention seeking behaviour ie to keep in the prominent position ahead of his sister. To make sure you are preoccupied with him albeit in a negative way. I'd say he's very jealous of your affection towards his sister so plays up to limit it by doing his utmost to command all eyes on him eg turning volume up, screaming in your ear etc. Best to try seeing them separately and hopefully that may improve things

BlueBelle

*He’s the only one I genuinely struggle with, and I’m finding it really hard to even warm to him*

….and he knows it, he knows you don’t like him that much, he knows you prefer his sister, he hasn’t at 6 got the verbal intelligence to sit down and say ‘ nan why don’t you like me’ so he does what many 6 year old would do he looks for attention, any attention he looks to disrupt and yes to give you a hard time as he feels you’re giving him a hard time
He’s good at school, he gets on with his grandad, so I d be surprised if he’s anything other than a little boy trying to punish you for not liking him
Change it around, play with him, have a giggle with him, kick a ball round, play a board game, draw with him, read an exciting story to him, find your route into him and most of all tell him you love him
I d have the children separately for a little while that way he’s not having to share anything you can give him your undivided attention which is what is begging for , he played his music louder and louder so you would know he was there a telling off is better than silence

I’m not blaming you just hopefully encouraging you to look at it through his eyes

I’ve tried to engage with him, his parents know he’s a handful, because he’s only needs a little excuse to explode and kick off, I don’t think he has anything like ADHD as he definitely knows when to behave. Very often when we visit they have to constantly ‘tell him off’.