It sounds like your best bet is to book the 2 cruises, 7 days each.
If the price is similar, you have more flexibility, in case of fare changes, air booking, etc. We do the b2b’s usually, unless it’s
higher to do so.
Also, you’ll have the same cabin and better choice of cabins, in your case if you book it as two 7 day cruises.
Won’t make any difference either on the App, as it will show one cruise, even though you book it as 2.