I haven't been on Ruby- only Sea- Princess, and I felt we had a very similar experience on the sister company, P&O. Even the decor in the cabins is done by the same firm, and the captains will talk about voyages they've done with both lines. One Princess ship will become the new P&O next year.
Ventura is a new ship, and whilst she is built with families in mind, the children are well catered for, and don't seem to cause much trouble- unless you're sailing over school hols., when any ship may be extra full of children, which has never been a problem to me.
Both ships were built in the same year, in the same shipyard and to roughly the same design, so it is only the interior spaces which will alter.
So, the balcony cabins will be roughly the same size; the number of decks and main dining rooms. Both should give a similar amount of luxury.
The main differences for you will be that Princess is run by an American company- P&O by a British one; the itinerary- because you're already in the Med, Princess will be able to make port stops immediately, whereas ventura will take 2 or so days to reach the Med ( for some, the best part of the cruise); One is in$$, the other ££; Princess charge $10 per person per day gratuity on top of your fare, P&O suggest what tips to pay; Princess charge 15% tip on everything you buy at the bar, P&O charge Brit pub prices without any tips.
I think you should read more on these pages before making your decision, as you really want a special holiday.
Enjoy choosing

Jo.