Hi Mulan,
I think that you are a saint for the sacrifice and love you are extending to your dear elderly parents. Just taking in one parent is difficult and courageous but you kindly take in both. An extremely loving gesture, to say the least.
I haven't read your full story but I can't imagine the elder's interfering with this arrangement in any way. It seems that they would be too afraid that THEY might have to step in and actually help take care of your Mom if they rocked the boat too much. God forbid they have to put their money where their mouth is and tangibly help an elderly sheep. In their hearts, they know you are doing the right thing and doing the best that you can in a difficult situation although they would probably never admit it. If they have the audacity to question the arrangement that you alone have had to come up with, then let them know that you fully expect them, her christian brother's, to actively help provide a better solution. That ought to keep them off your case! Apostate or no apostate, it's simply none of their damn business.
Wishing you all of the best!
CC