Do you like exercise videos, or zumba videos? you could do these at home and have the kids jumping around with you too. (might tire them out ready for a nap??)

Can you take a 1/2 hour walk when DH is home or when the kids are in bed ?

I am married to a shift worker too, sometimes it is good sometimes it sucks. If you know his shifts ahead of time can you write up a rough plan of times when you might be able to get out by yourself.

good luck