My son moved in with me...

So me and my wife just had a baby a few weeks ago. I have a son from a previous marriage and we had a falling put a year ago and didn't really talk much. I checked up on him and I do feel bad for not making more of an effort to fix our relationship. He was always for of a mom's boy anyway ever since he was a little. I just started to get the feeling he didn't really like me and as he hit his teenage years he seemed to just want to be left alone. 13 days ago I get a call from my ex wife's sister. My ex wife took her life... I knew she struggled with mental illness but I never knew it was that bad. Our son found her with her wrist cut in bed. Long story short, he's now living with me... Because of covid we can't have a funeral and had to cremate his mom. It has been really weird. He doesn't talk to me really and with having a new baby plus this on top of it it's been hard. My wife is only 4 weeks postpartum. My son won't eat with us he will only eat in his room and that really bothered her, so she told him he has to eat with the family and he slammed the door in her face and said "You're not my family." She starts crying and saying "So you're gonna let him talk to me that way?" I know she's more emotional because of postpartum, but my son is emotional because of grief and I dont like feeling like I'm picking sides. I don't even think my son wants me on his side. He wants to be left alone. I don't know how to be there for both and idk where to start on having a relationship with my own kid. It feels like I won't be able to keep everyone happy...