At least one of y'all speaks Rafterese in the family...
Before drilling holes in the NRS frame, I think Glen's idea of some cam-lock quick release nuts on the NRS kickbar would work really well for what you're looking for. That, with some pre-set marks on the frame for where the kickbar should go for each of you should let you to switch out in about a minute. Whatever you settle on it will be helpful to have a block of wood or rubber mallet handy on the river just to make it easier to move the kickbar into place (yeah, like you need any more gear when you go rafting...with kids...).
But wait, you'll also need to move the oar towers. Looks like you might as well just get another raft!
Let us know how it goes,