just talkin to them at the rite time only works for aeris n tifa, for barret n yuffie u hav to pik ut all the moments to destroy tifa and aeris e.g. wen locked in the shinra cells and tifa asks "can we get out" if u say "kinda hard" it will lower ur relationship by one point, so u can keep saying that like 100 times and totally destroy tifa.

for aeris, u hav to call her a slum drunk and do nasty things while she's around. if anyone wants all the steps PM me n i'll tel u, thers too many to puit in here, or u can just look it up on gamefaqs