Toffee being a Butterfly seems really unlikely now, if it was indeed ever likely and not just Toffee fans trying to connect him to everything. You can't really do the SECRET BUTTERFLY CHILD reveal twice (for the same reason, Marco can't be one either). It's still not entirely out of the question for Toffee to turn out to be connected to Eclipsa, for reasons like "how the fuck did he know about the monster temple," but there's not a biological relationship there.
Marco being a Butterfly is just straight never gonna happen because it's a fucking Y7 Disney show. You can't have Star getting horny over Marco and vice versa just to reveal, LOL THEY WERE RELATED ALL ALONG; it's just not something Disney would even entertain. And while you can argue they're really distantly related so they might as well be unrelated, the simpler/safer explanation is just "they're not related." Not to say people can't have theories or anything; that's just one I don't even bother to speculate on because it seems completely removed from what would actually be allowed.