without looking at each mortgage, the answer is you are probably safe
most note and mortgages to consumers are for individual pieces of property
however, depending on circumstance, it is possible to have a mortgage that covers both properties in which case your property would be at risk
If your brother's house is given as security on a loan that is also secured by your house, then your house may be exposed by the lender's foreclosure on your brother's house if the proceeds from sale do not cover the entire amount of the loan. If there are separate loans and separate liens with no cross-collateralizaton, your house is probably safe from foreclosure as long as you remain current on your loan.
The mere fact that both mortgages are through the same bank is not determinative of whether your house is subject to foreclosure. Good luck!