I can't speak to the upgrade availability questions, but here are some unsolicited suggestions:

If your husband has elite status with another airline, he should request a status match with Delta. That would at least give him the bonus miles that Delta gives to Medallion members. Your husband should hit Platinum or Diamond Medallion pretty quickly flying that route once a month.

https://www.delta.com/skymiles/about...ance/index.jsp

At the Platinum or Diamond level, he can request upgrade vouchers (called SWUs) which (as with mileage upgrades) are good only on Y, B, or M fares. However these can be waitlisted for day of departure such that he should get upgraded if seats are open. I don't know if this can be done with mileage upgrades.

Having said all of that, Delta is not a good program for those who want upgrades on international flights. The fare requirement is pretty steep in that the YBM fares are quite a bit higher than the deeply discounted coach fares. And the upgrade availability can be limited and difficult to work around.

But it seems like your husband will be flying Delta, so hopefully we can help you to make the best of it!

Take care,
David H.