buying out my sister's share in a 4plex - seller financing?

[Rose Dakin]

Hi there - thought i would ask the bigger pockets community in case there is someone who has done this before - I own a 4plex with my sister and ex-brother-in-law. they want out, so I want to buy their shares. they each own a quarter. i will assume their portion of the mortgage loan, but they also have some equity, i'm thinking about 40k to each, and they have agreed to carry that loan with seller financing over 10 years. but my question is, in this scenario, can the loan to them be secured by the property? if i stopped making payments to them, but kept them up on the official mortgage, how would they go about foreclosing on me, if they each only own 25%?

tricky. wish i just had a bunch of cash to pay it off right away. 

any ideas, let me know. Thanks,

rose