I swore I'd never post again after the bloodletting on my last thread - but here goes ---
Jeanneann ( JA ) -- I think you are a loving grandmother and meant to be helpful - but sometimes we do not realize the unintended consequences of what we do. I am a 60 year old MIL, so I definitely see things from the MIL perspective. I also have adult children, so I know what the teenage years are like -- challenging even with the best of kids.
I have to ask - is the kid a responsible delight and the parents are abusive and unreasonable? If so, then I'd probably take the kid in and decide that saving him was more important than my relationship with my son and DIL.
However, if the parents are responsible, reasonable, and the kid is just being a typical, defiant, immature kid, then I think that providing a haven for him when the parents are trying tough love is interfering with their discipline and the kid's need to grow up.
Sometimes parents are quite reasonable in kicking the kid out - look at the "No Good Deed Goes Unpunished" thread started by elsieshaye. Elsie has bent over backward for her son - he is abusive - and she has drawn the line and kicked him out. Probably the best thing she ever did for him. He will eventually realize that his actions have consequences, and that he needs to treat others with respect. If I were Elsie, and my mother or MIL had taken the kid in, I would feel that the GM had done an end run around me and my husband - that by providing a haven for the immature brat she was undercutting our efforts to instill responsibility in our kid, and intruding into our right as parents to discipline our kid. i would definitely chill towards that GM, who had yanked the rug out from under us as parents.
If the parents are not abusive, awful people, you might consider sitting your grandson down, telling him you love him, but his parents do too, and that this is between him and them, that you can't interfere in their dispute and relationship - that by providing him a haven it might appear that you have "taken sides" - and you would never want to do that. He and his parents need to work it out. He is (presumably) a young adult now - and that as a guest in his parents home he needs to respect their rules, etc - or go on his own - but not put you in the middle and ask you to take sides. Then an apology to son and DIL for accidentally interfering might be in order.
On the other hand, if the parents are abusive and awful, you need to provide the haven to the grandkid - and be willing to tell DS and DIL that his safety and emotional well-being is more important than keeping your relationship with them if it means you have to watch your grandchild submit to bullying and abuse.
Not knowing the kid or the facts - i can't say which it is - but I do think that when a third party interferes with a parents "tough love" - there had better be a very good reason.
JA - I am sorry this sounds harsh - I know what it's like to have good intentions but the other party doesn't see things the way I do. I just think the parental relationship is paramount, and you have to let them handle discipline issues with the kid unless there's real mistreatment by the parents.
Finally - I don't see this as just a DIL issue - I think she and your son seem to be together on this - so it's you vs the Parents (both of them) not just you vs the DIL
