I'd advise speaking to the naysayer and find out why he has a problem with an in-game tie between the two. Is he feeling left out or something? Two of my friends always seem to have their characters be brothers or the like when they play, and I just find it amusing, although I've heard people say they are jealous or that they now want a sibling in the game. One time, the whole party ended up split into groups of two that were siblings. I wasn't in that game but I heard about it.
Anyways, if the guy has a legitimate beef (from your point of view) then try to work something out with the couple. If not, then ask him to deal with it.