Rome to Munich - Double sleeper only for same gener?

Yes, the direct Roma-Muenchen night train is a CNL. With sleepers, whether they're one-, two-, or three-bed, so long as you book the entire sleeper genders can be mixed. So booking a two-bed sleeper for you and your husband should work fine. Book well in advance at www.bahn.de, not RailEurope, to get discount fares.

Thanks.

How many days/weeks in advance can I book my tickets? As we would like to book everything before we leave home.

Advance booking "windows" vary on the Bahn site. For day trains it's 90 days. For CNL trains it's usually 90 days, but it can be longer on some routes.

Here's the good news: The standard fare for a bed in an Economy Double cabin is €175, but the Europa-Spezial Italien fare is €99 and the Saving-Night fare is €79. Those discount fares are shown through 13 December. However, because new timetables will go into effect throughout most of Europe on 14 December, only the standard fare is shown from 14 December forward. When the new timetables are posted on the Bahn site, I assume that the discount fares will reappear.

That is almost 50% off the normal price. But is there any conditions on these special tickets? I think some only valid for return tickets not one way? Is that the case for the two type of special you referred to in your reply? And what is the difference between them?

Be careful when booking by raileurope.com the prices and availability change and you go through all the steps then they email you and say oh that price sold out and now its $150.00 more. We booked the same train for 12/25 and paid $310.00 USD per person for a Private Double Sleeper. My husband did not want to book the 6 ppl couchette but for the price I did not care but he was really freaked out so I gave in.

Yes, there are conditions for those discount fares. They are only good on the specific train for which you book them and they are non-exchangeable and non-refundable. They are single (one-way) fares and there is no advantage to booking return (roundtrip). The difference between the two discount fares I listed above is simply this: When the allotted number of seats are gone for the lower price, the slightly higher price may still be available. When those are gone, it's full fare only.