I'd be talking to the dealer. The XL tyres generally have stiffer walls and are the right spec for the vehicle. Honestly though, it's more for correctness than any worries it'll cause problems. They should retail a vehicle with suitable tyres.
That's the one. So you need a minimum load rating of 99 on the front and 100 on the rear, any lower is an MOT failure and you're also at risk of enforcement action if spot checked by the DVSA.
I'm not a tyre or van expert but doesn't this show you should have 235/50 R18 101W tyres on all four wheels of the vehicle?
The dealer may or may not have fitted them but they seem to have sold it with the wrong boots on and I would want them to sort that out.