Despite not concretely stating each other as "boyfriend and girlfriends", in EP8 Tremolo did tell both Josy and Maya that he's made the decision to be exclusive to them. I don't know about your personal perspective, but stating that you're exclusive to someone is pretty much a big indicator that you are boyfriend and girlfriend. And in EP10 as well, there's a few moments that allude to the the status of them being his girlfriends:
- when Tommy has his blow-up at Tremolo after finding out that he slept with Josy, he doesn't state it exactly, but he mentions that he's with both Josy and Maya. It's everyone else's interpretation that it's a three-way sexual relationship.
- when they're cleaning the upstairs dining room, after Tremolo calms Maya down, Melanie congratulates them and tells them about her own throuple situation, though that one was more about the sex, and when Maya asks him, he says that that's not their definition of their relationship.
- when Becky makes a shameless pass at Tremolo in the library, he does mention to them that he doesn't give a shit about Becky and the opinions of everyone else, that they know what they are and that it's enough for him.
So Tremolo choosing not to be up-front about the throuple with Neil would be weird, unless Maya explicitly mentions to Tremolo that she wants them to hide the situation.
Otherwise, the throuple are pretty much official, it's just not a publicly official situation because reasons.