Hello Adgm. It appears from your posts that it's your s.i.l. whose the problem here, and possibly your D too if she says nothing when he's letting the children into a room where you've put your dogs, and does nothing when the children are chasing them around the garden etc.
I think Redhead's right that your s.i.l. is provoking this situation to wind you up and if he is, he needs to grow up and take his parental responsibilities seriously.
Children need to be taught as early as possible to treat animals with kindness and this doesn't seem to be the case with your GC.
This is your home and for me it has nothing to do with you prioritising your dogs over your GC. You took steps to keep both animals and children safe and this was undermined by your s.i.l.'s juvenile behaviour, which doesn't appear to have been challenged by your D.
A conversation needs to take place before the next visit in which as NotSpaghetti's posted includes you telling them how stressful and anxious you were, trying to keep the children and your dogs safe.
Before the next visit, tell them what arrangements will have been made for example, which room the dogs will be in which the children are not allowed to access. When the dogs are in the garden if the children wont stop chasing them, the children will have to stay indoors. If they pull their fur, ears, tail etc they are to be told firmly to stop.
Of course you love your GC but you love your dogs too and learning how to treat animals with respect and kindness is something all children need to be taught, whether there are pets at home and/or at grandma's or not.