Responses
Maybe they didn't spend ruts together, with him being originally a beta it could be difficult (maybe that's the reason?). They surely had sex but maybe not during cycles of rut
Also his hubby probably didn't pump the place full of his pheromones, that's a big part of the reason he changed to an omega (if I'm not wrong)
So, the hubby respected his husband's identity as a beta man and didn't need him to be anything else than himself
Anyway that's my thoughts on the matter xd
Why didn't step dad become an omega in the decade or however long he was a step father. I'm sure he spent multiple ruts with his husband before he died.