+1 on the weeride, my eldest loved it and now his little brother is in it and loves it too. You do have to ride a bit knees out, but it’s unlikely you’ll be going too far/long and the benefit from having him up front far outweighs any discomfort.
Only issue for me with the weeride was the big/heavy mounting bar, you can take it on/off but seemed like a lot of faff so I stuck it on the wife’s hardrock and used that.
You should be fine with reach also, although as my eldest starting getting bigger I put an adjustable stem on the bike to bring the bars up a bit and give him some more room.
I wouldn’t get a rear mounted seat, I recently got a second hand Hamax for the eldest (2.5) and neither of us liked it. He was totally disengaged, going from chatty and excited in the weeride to asleep in the Hamax. The whole thing felt unstable and swung the bike all over the place (old steel framed MTB so admittedly flexy).
I was lucky enough to find a LOCT seat for the eldest, picked it up at the weekend (thanks Jason) and took him straight out. He’s back to his normal self on the bike – jibber jabbering away, pointing, etc.
Bottom line – get them where they can see what’s going on, it’s much more fun for them.