Husband and I have very different style as grandparents

I think the children need to abide by your rules when they are at your house Phillipa
Fighting and unruly behaviour is not acceptable. I really don't understand this idea of it being the parents role to discipline the children if you are caring for them. Children need boundaries for several reasons including safety.
The way they are disciplined needs to be agreed by parents and grandparents to ensure continuity.
The idea if not having all the grandchildren at once or you taking them out for a while is a good one. It will reduce the stress levels for your husband.

Phillippa, Iv read both your threads, and I'm still not sure what you're calling "lack of discipline." If it's just long hours on electronics, imo, that's up to the parents. If the kids are being rude to you and h, etc., you have every right to object. Also, I think if they're doing something in your home that you don't like, such as jumping on your furniture, you can certainly take the "grandma's (or grandpa's) house..." approach.

I don't blame h for wanting to step in when the kids are fighting, especially if they're getting physical. But if it's in their home or the parents are present, it's the parents' job to discipline them, not h's. If you're babysitting, imo, then he can say/do something. Imo, when one is watching someone else' kids, discipline becomes part of one's role, at least a little. He may need to find a better way though.

Also, if he tries to discipline your gc when the parents are there, THEY need to speak up. You've tried, but to no avail, and it is really their call.

My husband is the same. Bad tempered, shouts if he considers they are misbehaving and even hit our eldest who has quite challenging behaviour. I was horrified at his outburst and now try to see them on my own or they visit with parents. I have probably over analysed H behaviour but think he is jealous of the GCs. just after our eldest GS was born my H withdrew from all intimacy with me. My DS and DIL excuse H's behaviour as artistic temperament. I am not so forgiving. We moved house to be nearer to and involved with the GCs and I want to enjoy being with them and for them to feel safe and happy when they are with us.
My advice to you Philippa 60 is to try hard to find a common ground between OH and GCs - animals, nature, model building, painting, writing a storybook, gardening, cooking, maybe he could take the eldest GC shopping, both mine love to have a shopping list and go round supermarket with basket and their own list. Try and keep the children occupied some large A2 sheets of paper and pens will fire their imagination. Our GCs love playing shop, a shop each of course, they spend hours doing signs, setting out their wares, counting money ( real money is fun). They always help with lunch or dinner especially the serving . Try and take the GCs out for exercise and leave H to rest for a couple of hours. Another suggestion is to have the children separately at times, one child and the lack of boisterous behaviour might help H bond with each in turn.
My H's relationship with the boys has improved but like you I am always on edge. will never trust him alone with the GCs. Unfortunately his attitude has caused a big rift between us but having thought long and hard about our relationship think the rift has always been there.
My next bit of advice is try hard to sort the problem between H and GCs , concentrate on the qualities you love about your H or like me you might find yourself contemplating divorce. Drastic step after many years of marriage but I see my H as a man who has cultivated lots of time consuming hobbies so he can use his artistic talents to withdraw from normal life and excuse his eccentricities and temper tantrums.

I think quite a lot of older men are like that, grumpy and impatient with children, as the kids get older he will probably find them easier to do things with. If they are fighting I guess they are boys, one of my neices has 3 in that age range they are terrors, no way would I have them.
To keep the peace it is best if grandad has another pastime to occupy him, gardening, fishing, golf, DIY, anything.

I think that discipline in your house should be set by you.

In the children’s house it is set by their Parents.

If they are fighting then I’m not surprised he’s cross about it, if you aren’t allowed to discipline them whilst they are at yours then maybe they should be with you less often?

flexiblefriend
Completely agree with you,

Are they fighting in your home or their own? Your husband is entitled to tell them to behave in your own home. Why should he be expected to put up with their rowdy behaviour if he doesn't like it. I hate kids screaming and hollering and fighting is a complete no no. It's doesn't sound like a lovely time in your lives to me, either the kids are fighting or you and your husband are. Tell the kids their behaviour upsets grandad and makes him mad, that they need to stop fighting and arguing when he's around. If you put up with it that's up to you. Maybe he'd have no reason to shout if they were better behaved and he might enjoy their company more if they were more pleasant to be around.

"pull them appart when they are fighting"

I basically disagree but manage to keep it to myself. H disagrees but cannot behave nicely and kindly with them. It's more about HOW he interacts with them, he shouts and on occasions can even grab them roughly to pull them apart when the kids are fighting. He's not actually violent, but aggressive for sure.
I find that I have to play "good cop" to his "bad cop" all the time.
It's so hard

On your other thread you describe how you disagree with your daughter as to how to discipline the children. You now appear to also disagree with your husband about how to interact with the children.

I'm sure you only want the best for them, but perhaps need to find a middle ground somewhere.

Tell him that as it causes rows he will have to be out when the grandchildren are there. He may be unhappy about it but the four of you will not, better one unhappy person than four.