Sarahz your op takes me back, (demanding they chose the name, religion (theirs), constantly 'my baby', smothering, phoning all the time etc)
I feel for you, but it is worth stopping this behaviour as it can effect your whole family negatively (in my case with my dh!)
My advice is involve your dh, I backed away and put dh in the middle as a buffer.
He needs to help set some boundaries.
How often to you see them?
I now also do what Sakura does, ds goes either by himself or with dh. I try and avoid contact, it's better. I no longer have any concerns about their influence as I know they can't undo the rest of the time that ds is with me. Plus they do have a relationship with him and that's fine. (also in my case it's just mil not fil, whom (?) I like alot - so want him to see ds.)
(Sakura I always like your posts on mils they are a comfort to me, I just wish it didn't take me a year to find mumsnet, the stress in our family probably wouldn't have been so bad!)
Good luck , let us know how you get on.