Are you eating with them?
Yes we’re always eating with them
All of that behaviour is developmentally normal. I would just let him graze. As long as he is eating something, I don't think it matters if he sits still to do it.
I had the same issues with my son around that age. We now use a booster seat and eat all together at the table. that has significantly improved his reluctance to stay seated. :)
My daughter does the same , take a bite then run or walk around , then again bite...no advise, sometimes she can sit for a while to eat but not often