MXP and rail....

MXP to Milan's Central Station is served by regular and convenient motor coach service, big buses with baggage lockers beneath, discharging in a drive just outside the station's main entrance, but badly served by ramps for rollaboards, IIRC. "Train" service from MXP is to a suburban station with an easy transfer to Milan's CS.

The trip by rail from Milan to Monte Carlo is scenic and interesting, and likely just as comfortable in 2nd Class as in !st (and cheaper). Planning the portability and "liftability" of your baggage is the key issue. If it don't roll, it needs to sit atop and be attached to a bag that rolls, and both man and bride need to be able to pull and tote. I haven't been in MC's rail station in decades, but recall it as a modest "through train" sort, often requiring descents to and ascents from below ground corridors from outside tracks (and with my luck, my trains always run on outside tracks, never adjacent to the station platform). No problem, as long as elevators/escalators are working, more likely in MC than is cities of lesser renown.

The entire evolution will be simpler and easier upon mind and body, than would be the proposed alternatives or other adventures in travel.