3 seaters for kids
Chuck;
It’s rather easy to make a three seat rear with the -10. All you need is a cover over the center that attaches to the seat pieces on the bottom and you add the extension with a L bracket and aluminum piece to fill the area on the seat backs.
I had a 14,10 and grandma in back seat with no issues for room, yes it was tight but the trip was short, for your three, younger, children it would be no issue. You share the attach point for the two seats to add another set in the center, the shoulder harness is pretty much a duplicate of what is done for the two back seats, just add another point. It can be done and it can be easily within CG. It took me 4 years to build the plane, my kids where about your age so, again no issue with size when completed.
Now my kids are older and we limit the flight to include my youngest friends, but not my oldest as they wouldn’t fit “safely” specifically probably see punches for space issues... but with that said two fit comfortably and one can lay down across the full 2.5 seats if only one is in back.
Personally I would do it again, there has been so much more benefit to having it across than two seats.
As for my seat layout. 1.5 seat and 1 normal seat- or one seat covers the full and gap and the other regular, that way I can still pull down one or the other side for storage expansion.
Sorry can’t locate pictures but send me a PM and I’ll see if I can send something when I find it.