Purchase family house after sister died?

[Jacob Northfield]

Hi folks, 

I recently closed on a duplex in Rochester, NY which I was planning to househack. My plan was to move in June when the lease on my current apartment was up. Unfortunately, my sister died unexpectedly a couple of weeks ago and our family is in NH. She was previously living at my mother's house while my mother is living elsewhere. She left behind three children and I would like to either gain custody or help my mother raise them in our family home. I have a couple of questions on how to best make this happen. To preface this, my duplex assessed at 175k and I purchased it for 152k. My mother's house assessed at approx. 400k but she is willing to sell for 300k. I can only afford about 2,100 in rent, though, which doesn't seem to be enough for this property with today's interest rates. What is the best way for me to handle my duplex and finding a way to move into her house while putting it in my name? Basically: 

1. What do I do with my duplex? I just bought it last month and have not had an opportunity to rehab because it's currently rented out so I'm not optimistic about selling. I was thinking I could fix up the one apartment and keep the current tenant in the other apartment then manage it long distance, but that would deplete my cash flow and possibly cut into my cap ex at the moment. Initially I was going to focus on MTR which would compensate, but I'm not sure how difficult that would be from NH.

2. How do I buy my mother's house since I have just signed on a mortgage? She has only a HELOC, no primary mortgage, but the house needs a lot of work. My goal wouldn't be to flip it, but to add an in law apartment in the basement so both my mother and myself could live there in separate units, one of us with the kids. I don't know much about creative financing but I'm willing to do the research, I mostly need a point in the right direction for this one, I think.

Thank you in advance for your help.