My children have always known our gay friends are gay, they have never questioned it, in their lives some people are with the opposite sex, some are with the same sex, it is just normal.
I would of thought pretending would just lead to more questions, "Why hasen't Dan got a girlfriend, why does John share Dan bed?", "Why Kate kissing Sarah?"
Children are experts in human behaviour, they lean by studing adults, so any astute child will soon suss there is something to focus on,
Children always know when truths are being concealed, they just don't know what to do about it, so it makes them uncomfortable.
As for making your friends conceal a part of their lives, because you haven't address your own issues, that is totally vile , what good friends they must be to go along with her nasty behaviour, but it is a really unhealthy thing to do for everyone involved.