seller financing tax and contract help

[Royce Talbo]

this lady i met is 76 years old has a condo rental she bought in the 80s. she said she doesnt want to sell because of the huge capital gains tax she will have to pay. (bought for $110k, my offer price is $550k.) instead she said she is just going to rent it out till she dies and her brother will get the property and he can sell it or continue renting it out. 

I want to offer her seller finance deal so that she can still get monthly income and not have to deal with taxes. from what i understand taxes involved are recapture tax from depreciation, capital gains from monthly installments and regular income tax for interest. 

I would tell her to use part of the down payment to cover the recapture tax, keep the monthly installments and down payment to under $41k/year to keep her in the 0% bracket for capital gains and what ever we decide on interest for the regular income tax. does everything sound correct so far?

Now the main question when she passes away, I want to write in the note that the brother can continue with installments or I have the option to refinance and payoff the mortgage. is this possible to have her brother involved or is this something that she has to write into her will/trust or whatever?  remember she doesnt want to pay a huge capital gains tax so a balloon payment after several years is not an option. so how should i write it so that i have the option to refi after her passing?

also how does it work for his taxes if i do refinance after her passing? does he have to pay capital gains on the remaining amount?