In my current cong., lesbians are there but they deny their relationships (to the brothers).
The elders are not usually going to get involved in these situations because
there are not 2 eyewitnesses to any sinning, and they are very uncomfortable
trying to "out" anybody as this could backfire (make people think the elders are
extreme control freaks).
In your situation, the added burden of what to do with the sister comes up.
If they insist she leaves the "worldly lesbian roommate" knowing that she is
disabled and without family, the congregation would truly be responsible for her.
That would be great if they wanted to live up to their responsibility, but they virtually
never do want to. They will view you as somebody their sister can take advantage of-
a worldly person supporting a sister in her ministry. But truly, they will most likely
overlook the situation because they don't want to care for the sister, themselves.