Step son doesn't have to eat with the family

My family ways ate together together and I expect my kids and all of us to eat as a family too. Things are a bit difficult because now I have a blended family. We try to keep a lot of the rules the same for our kids because we don't want to cause sibling rivalry. The only one my husband's bends rules for if my step son. My step son mainly lived with his mom but she went to jail so he lives with us now. I always tell my kids they have to eat at the table with us unless they are sick but my husband let's my step son go to his room because he's "having an episode" but he never explains what that means. I don't know much about my step sons mental health. I do know he's on medication but my husband never goes into detail. So it just looks like I'm being unfair. If he's having an episode I think being around family would be good for him but my husband says no and hes his father and he knows him best. He hasn't even lived here the last 4 years. But whenever he is having an episode my husband just lets him eat in his room and my kids find it unfair.

Edit: Whenever he has an episode it's random. Sometimes it's at dinner. Sometimes it's at school. It's unclear why certain things set him off