I know how you feel!!!
All I can suggest is:
Do their sleeps coincide at all during the day, if so this is the perfect time. When my son was on 3 sleeps a day he and his sister were asleep for about an hour at the same time, so I used to take the first 30 mins to sit down with coffee/ lunch etc and a magazine or the TV and just RELAX. Now that he's on 2 sleeps, they're never asleep at the same time, so I praise God for the invention of the Jolly Jumper!!! That at least takes care of the little one, and when he has his time in it while Em's asleep, that's my time.
Otherwise things like getting hubby to take them both for a walk so you can stay home by yourself.
Or get them both minded by hubby/ a friend etc, so you can go to the shops for a walk around, coffee etc. Even if it's only for half an hour it make a huge difference.
When they're both in bed at night, run a bath and take a magazine in with you and stay there for ages.
These are the sort of things I do, hope they can help.
Kellie, mum to Emily 4yo, and Jack 21mths