Feeling lost!

So my husband is trying to sponsor his widowed sister and her 2 kids and their mom to come live with us under 1 roof. Fine I can in a way understand but the problem is that I'm terrified of his mom who stayed with us last summer for what should have been 2 wks but became 6 months and we live in a 1 bdrm apt! In that 6 months she almost ruined my marriage and constantly got on my case that I have a problem thst I haven't had kids yet. Now my problem/question is today my husband told me he wants me to sign and get notarized a letter to sponsor his sister. I am on a business account of ours so that's why but when I asked to see what I will be signing it's created a huge fight. I don't think I did wrong as I can't be held responsible in future for his family. He also needs to share with me if he wants me to accept them which I have. Now he's having me removed from the business account which is fine as I was already wanting that due to tax reasons but the fact thst he tried to remove me immediately hurts! I feel like my marriage is falling apart because of his family issues. I also have an iui procedure coming up and I feel completely lost now about this.😢