My first seller financing (And I didn't even know it)

[Roy So]

Need a bit of advice on this... Here's the situation.

About 5 years ago I took over the mortgage payment for my mother's house ( I don't live there, currently renting an apartment with my wife). 

I never realized this was basically a seller financed deal until BP.

The house is on Long Island, and worth probably about $450k currently.
At the time I took over the payments there was about $200k still due for the mortgage. (now the balance on the mortgage is about $150k), payments are about $2,000 a month including taxes/insurance. I also pay her utilities.

The thought was that my mother (who's not working) will live in the house as long as she needs to and the house will be mine after that (my mother is 70).
I have 2 older siblings who are not involved in this situation, part of me is afraid there would be some animosity in terms of inheritance one day if we don't sit down and discuss this soon...(when I have the house and they don't).

Plus side: I didn't put anything down, and am just making the payments. My mother doesn't have to stress about payments every month out of her savings.

"Down Side": no income coming in for the (hopefully very long) foreseeable future.

My question... Is there any down side to changing the house deed to my name now? I used to be against that idea before I was on BP, thinking it may come in the way of me getting a mortgage one day for my own home/investment... but now I realize that as long as the mortgage for this house is not on my name then I should be fine since I'm not officially taking on the debt? does that sound right?

What would be the costs associated with changing the deed to my name? is it even doable?

The rate she has is about 5.8% (this was a no-doc mortgage) but I feel like I should be happy to have that rate considering it's not in my name.

I may be wrong about a lot here, please let me know.

Thanks in advance.

Roy