My understanding about the castle is that it is a total money pit. They tried to sell it a few years ago, but there were no takers, so now they rent it out for weddings, corporate events, etc. They also go and stay at the castle some weekends, holidays, etc. I guess they either have a manager who stays there permanently or an arrangement with locals to take care of the place and run the events.
Damien Lewis is married to the excellent Helen McCrory, who I'd be utterly terrified to cheat on, but mostly because of the characters she plays. I'm sure she's lovely in real life though.