Ultra possessive grandparents?

Cuffetta99

We just had an upsetting experience. Yesterday was the first time we saw our grandson together with my son in laws parents. We used to be good friends with them for years until the baby was due. I was a birth partner for my daughter and this was not well received by the other set. Some comments were made which I rose above thinking that it was just a bit of jealousy.
Then lockdown started and we were my daughters support bubble. So the other GP didn’t see or have contact with GS apart from outside at a distance for 18 months.
So we’re both really close to him, I see him 5 days a week normally. My husband (step dad to my daughter since she was 11) sees him 2/3 times a week.
The problem yesterday. We were nervous that GS might be too obviously confident with us and too shy with them. Since C19 has been almost all his life (20months) he’s very shy of people except us and his parents as that’s all he’s really seen.
But not only we’re our fears unfounded but reversed!!
He’s seen more of his other GP in the last few weeks so is more comfortable with them. But yesterday was weird!
He ignored his other Granny, mostly because he was utterly monopolised by paternal GD. He picked him up immediately on coming in and that was it!
(He has other GC which he’s always done the same with ie takes them off to play away from everyone else (including his wife) and totally excludes everyone else. His other son (parents of older GC) eventually told him off for constantly taking first one, then both GC, away from the family group saying he wanted to spend quality time with his kids as well on a weekend as he works all day and obviously only sees them after work most days. I don’t know what the response was but it still happened. Till they got fed up with it and supervised their time with them more closely and stopped him taking them off.).
So this happened again yesterday. GS was totally just wanting to be with GD and play etc and ignoring his parents and us. So maybe we were just surprised and a bit confused to start with. As the visit went on, he took him off up the garden or in the summerhouse or up to the allotment several times. (GS is never not wanting to visit the allotment ). Son in law got the “go with them” look from daughter as she doesn’t trust him not to have secret snacks of chocolate to give GS.
(They both (other set of GP) think it’s funny to give GC chocolate and treats and the older ones are sworn to secrecy ie “We mustn’t tell M&D we’ve had chocolate/money to buy chocolate/biscuits “ etc because we’re not allowed it unless they say so. Which we all think is appalling and daughter and SIL have shopped them to the other parents about. But despite threatened sanctions it still secretly goes on ).
So when eventually GD left the room, I was talking to GS and asked him if he wanted to show other Granny a toy. She was very keen to share it as he hadn’t been near her all afternoon.
GD came back in just as he moved towards Granny and sat on the floor in between GS and Granny and asked to see the toy. Distracted again and then taken off again to look out the windows.
So I’m well aware this sounds a bit petty but why is he doing this? Why does he have to monopolise any child and remove them from the group for 121 interaction? What’s going on?
As my husband later remarked “ no one else need have been there! It created the most odd atmosphere “?
He was very upset by it and couldn’t understand it at all. I’m also a bit confused as to why he does this? He’s a bit of a show off and a confirmed liar but this is still odd behaviour. I felt so sorry for Granny but she always lets him walk all over her ( and his kids) without demurring so it’s not surprising that he gets away with it. My husband said he’s shot himself in the foot as they won’t be invited back when GS is here, so he’s the one who’ll miss out. I don’t know if confrontation is the answer or not. (Not from us, I’d have no problem doing it but it’s really a parenting issue). My daughter has only just accepted they have to see more of them now lockdown is eased but still has trust/dislike issues with them because of serious lying/honesty/causing her husband pain issues from long before lockdown.
Does anyone else have any experience of this?
I’ve read a few articles to try and get a handle on this but would appreciate any constructive advice please?
Just to add, 2 days before, GS saw his great Granny and some other relatives for the first time in 18 months. After a shortish while of shyness, he lost his nerves and had a lovely day playing in the garden with everyone. He was the centre of attention of course but played beautifully with all and it was a lovely relaxing day. Not one person tried to fight for his attention, everyone was just happy to share a lovely day with him.