Are my puppies becoming ual?

So I got black lab puppies. They are about 3 months old now. My family and I have had them for quite a while now. They are brother and sister. 4 days ago the female (jess) tried to start the male (duke). My mom was close by so she pulled her off of him before she actually fully got on. She then tried it again the next morning. Then yesterday Duke tried to get on top of Jess. We have always pulled them apart before one of them could actually start . Its way too early to get them spayed and neutered yet. And why is Jess trying to hump Duke? Is it dominance or something? Please don't tell em I have a gay dog. Not that it would make me love her less if she was. But yeah. Please explain! Thanks in advance!