The croch belt is not needed but can be used the stock seats have a short front and the croch belt is to keep you from submarining ie. sliding out of the harness. I use a rollbar to attach the sholder belts but not sure on a 2+2 guess you would have to attach to the floor pan in footwell not real good for passengers.
And as for bashing you I was trying to help you with some info if you took it as bashing sorry guess maybe your a little gunshy so I will let it go in the sprit of getting alonge :)