I don't want to have a flower girl or ring bearer
That's not good, why don't you want to have them in your wedding?
I don't think they are necessary.
It is your choice if you do not assign any ring bearers or flower girls, but your family may be hoping they can make their young family members to be either ring bearers or flower girls. Why not still have ring bearers and flower girls as no harm will occur if you decide to have them.
I don't, I think it's fine without them. I didn't even want invitations or a wedding party.
I think I have said enough and it is ultimately your choice to not have them. You may be disappointing some friendly members of not having flower girls or a ring bearer, so I do hope you talk to them before you decide on doing it.