Given that €1,000+ pps would not be unusual for a two week self catering holiday in parts of the Med without the cruise part €1,200 for a cruise and presumably including full board etc. seems a bit low to me. But then again I've never been on one so don't really know. Have you checked the brochures and rung around the travel agents that do this sort of thing?
If the olds are up to a connecting flight to the UK, I'm sure Thomsons, amongst others, can do you a cruise for less than the €1200 each. www.thomson-holidays.com
I had a look just now & saw several 7 night cruises for around €1000.