I can use a couple different ways actually. I have a seat that attaches on the rear rack and a trailer that I can hitch with capacity for 2 kids plus a trunk for extra stuff.

Recently though we purchased a front load cargo bike which comes with bench seating for 2 kids and we can get an optional extra bench for a third. We could also put a rack on it and have an additional kid (or stuff) on the back as well. Technically we could probably hitch the trailer to it as well but I think that would get a little impractical at that point since it's already pretty long so the handling with the trailer probably wouldn't work too well