However, this is the first time I've bought two Societies as a pair & the first time I am having trouble sexing them - well at least one of them; the chocolate crested. I am *almost* certain that the white/brown pied is a male... he sings A LOT

My goal was not to have a breeding pair necessarily, but I want to be be prepared for chicks just in case! In the past, I've always kept my Societies with mixed species and never worried about it until now.
I know its hard to determine the sex of Societies from description alone; really I have a few questions and clues that maybe I can find help for:
-----It's been a month since I've brought them home and still no chicks. This makes me think that they are both males. BUT, I've never seen or heard the crested finch sing - it's a fairly quiet little guy. Is there dominance among male Societies, meaning if one is outwardly male (the white/ brown pied) and very pushy will the other one - if male - be submissive?? (I have no idea if there is such a thing with finches.) Or do males ONLY sing around females (I haven't ever really found this to be true, but I could be mistaken)
-----If the crested is female, and they have not (and will not) mate, does that mean they could be siblings? They get along very well.
-----Both birds have contributed to adding bedding to the nest they sleep in.
-----the crested's chirp is sometimes more of a purring sound. He's more submissive and less hyper.
-----the white/brown pied tends to sing/warble most when he's on a branch alone, sometimes in front of their mirror.
-----they like to eat and drink together.
-----the white/brown one loves to get preened by the crested and its the only time he's really submissive toward the other one.
-----both tend to start small brief pecking fights with one an other, but rarely.
-----there has been no attempt at mounting or mating that I've seen. And I watch them a lot!
I'm really not sure what else to add. Anyone have any ideas or suggestions on what to look for?
[Here's a photo of the little cuties. Their tentative uni-sex names are Bumblebee (white/brown pied) and Tumbleweed (the crested).]
Thanks!
~Misty