Unfortunately the deposit side is tricky and really between you and the dealer. Motability advised me previously to not place a deposit if I can help it, easier said than done at most dealerships…
Personally I would expect the dealer to go or the price drop in AP, the change for motability per poses is trivial and a few minutes work for them. In terms of getting the vehicle before the baby arrives, have you asked if they can get a hold of anything within the dealer group? Most dealers have orders for vehicles that are expected within weeks, if not already at a location and not yet purchased or held. Well worth asking about this as an alternative to a lengthy wait, options might be different and colour of course, but the dealer may be more open to a change that way vs cancelling and arguing about your deposit refund.