sry to hear that, but i think it is too much for your sis to blame you for what happened.
but she might be very upset thats why she say such things.
just that imo, given the way you say about her being so heck care, i doubt she even got bothered about your bro's problems but just finding someone to blame (but herself) for the miscarriage, and just nice you happen to "appear" so she just conveniently put the blame one you. it is not your fault, n perhaps not hers (if she didnt do anything wrong) that the MC happened. it can happen to anyone. dont blame yourself.
if they dont bother about you, i think you shldnt waste so much time on them either.