I don't think anyone here can make a qualified decision, I am sorry for your loss and I wish the situation will sort itself out. Try finding a counsellor, maybe a free one or someone who you are really close too. You are probably feeling like you are being replaced, I used to get that feeling when my mum took in a homeless friend of mine, I didn't mind it but he had ADHD and would sometimes come home from the pub blisteringly drunk and wake me up and its a small bungalow with maybe 7 people living in it. It shouldn't matter if you don't see eye-to-eye with the new guy and his children, just make an effort to be supportive.