Levi's journey so far: he has met Matt and Luke and has broadly accepted their relationship (with some reservations), aided by the fact that they are family. He has also met Tim and Guy but they are not (yet) family and he finds their relationship much more difficult. He still has to meet Tony and Aaron, Scott and Justin, Zack and his partner (if he has one), Jess and Kellie... The whole works, in fact. So if he is going to stay with Matt and Luke he will have to make his peace with same-sex love.
Of course, that leaves a range of options and it will be interesting to see where he ends up. We don't know anything about his own preferences yet, so we can't rule out his finding himself a boyfriend and living the life. Maybe. Otherwise he can wholeheartedly accept it and be supportive, accommodate it and just feel nothing much about it or (at worst) tolerate it. Toleration, of course, is not indifference; it's opposing some aspect of another person's behaviour or beliefs but accepting it because you respect the person. It's hard going so I hope he doesn't end up there. (Don't get me wrong - better toleration than hostility or hate. It's just not a very positive state of mind.)
Meanwhile, Tim and Guy aren't engaging in PDAs as I understand the term. They are not "in public", they are in their own home. The four guys are two couples, not a group marriage, so by their own rules some things are kept behind the closed bedroom door, but that's their joint decision. The four of them may choose to modify their rules slightly if/when Levi becomes a member of the household rather than a guest but it's four to one (and the four are the owners of the house) so I'd expect 80% of the movement (at least) from Levi, not the others!
I look forward to future developments.