"Halfbreeds"?
Would you care to rephrase that? It's considered a racist term.
B'Elanna is hybrid. Seven is not, as she had two parents of the same species.
I can't imagine Voyager even beginning to approach the finesse of Xena: Warrior Princess as far as lesbian subtext is concerned.
I don't remember which episode, but there's one where Seven states that she doesn't want to limit herself. It seems obvious that she's willing to experiment with anyone, if she finds the individual who would meet her exacting standards of intelligence, common interests, and so on. Gender and species would be irrelevant.
I think eventually Seven and B'Elanna could become good friends, but with no romantic/sexual attraction involved. Just friends, and it's a shame that wasn't allowed to happen. TNG and DS9 both had two women as "buddies" (Crusher & Troi and Kira & Dax). Even TOS had Uhura & Christine Chapel. The Voyager fans got Tom & Harry as the buddies, but none of the women characters developed that sort of friendship.