lets put through a hypothetical question then.
IF your parents view being straight as unacceptable to them(dun ask
me why the hell they would think this way, its just a hypothetical
question), then would u be lesbian to please them?
while no doubt most parents in this world often want the best for
their kids, have you considered that they often view things from
their point of view, which may not neccessary be the best point of
view for situations happening to YOU?
this here now, is the question of, would u go against your parents
to stick to what u believe in, or value, or would you drop your
freedom of choice to please your parents?
no doubt it is a tough choice, but who lives with the final
consequences of their choice? you. everyone has the right to choose
for themselves, because it IS everyone's right as a human
being.
i would feel that if u are truely worried about your parents being
heartbroken, hide your sister's lesbianism from them. give her time
to sort it out herself, and if she chooses to be a lesbian, so be
it. its her choice, its her life. respect it even if you do not
approve. but for the time being, the best solution i feel, if u do
not want to totally alienate yourself from your sister, and yet not
upset your parents, is to simply hide it all from your parents, for
the time being.