Would I be wrong to stop my eldest son seeing his dad?

I have a 4 month old with my partner and an 8 year old from a previous relationship. My 8 year old sees his dad twice a week but his dad and all of his family don’t stick to the Covid rules. They all (his dad, nan and aunties with all their own families) still see eachother not socially distancing and we are in tier 4!

I have told him multiple times to be careful, especially when he has my son as he will be coming home to me and the baby, and I have my baby to think about on top. He hasn’t listened. He had him last night, but said he was staying with his mother and then his sister drops my son off?!

Not to mention a couple months ago when my son was with his auntie (dads sister) they got positive corona results 2 days after and therefore my son had to isolate for 2 weeks and I had to keep him away from baby..