Oh my word, what a terrible situation. To answer simply, yes I do think it’s because of your grandsons parents. Your daughter is clearly not well, worse than not well, that and his dad being gone along with all else has all impacted his life and emotional state. At the beginning of your post I thought how rude it was for your daughter to just show up with all her belongings like that, but thank heavens that she did, your grandson needed you desperately.
I’m sure you know but don’t let him alone with the dog, give the dog some extra love too after being hurt intentionally (even in a minor way) and having everyone move in your dog may be confused and lonely (can you tell that I love dogs )
Don’t have much time to write but I wanted to express my sympathy, you have had a lot dumped on your plate suddenly. None of this sounds even remotely easy, you must be a very strong woman to have weathered this storm and still be standing tall for your grandson.
I suggest that you find out if you have any legal options, whether that is asking your daughter for temporary guardianship of your grandson, or petitioning the court for it because your daughter, at this time, should not be around her son. She needs time to work on herself with a professional. Also, can you get your grandson to a counselor? He desperately needs it, he has to have some outlet with a professional, he is suffering the most from this chaotic mess. He needs your stability and guidance right now, please get him into whatever services you can, now may be the only chance he will have for an adult to truly help him with all his trauma.
I’ll have you in my thoughts, I can’t remember if I said everything I wanted to say, I hope this all will suffice! Also, so sorry for your daughter also, I can’t imagine what she’s going through right now. Remember to do some self care for you, you need to be as well as possible for your grandson right now! You are amazing!! Good luck