Fixed males aggressive to pregnant female

My two seal point siamese boys who have been fixed for 1 1/2 years are being mean to my pregnant female. She isn't antagonizing them or anything. My only guess is that she is giving off a smell they don't like?? They don't have a mean bone in their bodies, but the last couple weeks they've been not so nice. And, they don't do it all day and night, just maybe once a day or less.

Any ideas? advice?

Thanks!

It's not uncommon for entires and neuters to get a bit upset with each other. I'd separate them, especially as she's pregnant.