It is apparant how they feel about you and your husbands wishes and feeling when you said they "just paid off all of their credit cards and are broke again. They took the opprotunity you gave them and used it as a way to pay off their credit cards, instead of doing what they said they intended to do. That's called taking advantage and disrespect.
You have three choices here,
1. Sit your father down and tell him you love him but they have x amount of time to get their together, and get moving. This could be whatever you think is fair, one month to a month and a half to 2 months.
2. Tell them that you don't appreciate them paying off their credit on your dime, and they have two weeks (three weeks, one month tops) to get out.
3. Give them the money, which is really sad since you've already given them so much, but this could literally have them out in weeks. Providing the stepmother can agree on a house she likes, which in my opinion she will probably drag this out as long as possible too.
Whatever you decide, you have to talk to your husband, make sure he understands and is in agreement with you to put your combined feet down. I would also be sure to tell your father how you feel about the whole thing, if for no other reason that to get it off your chest.
Let me know if you want to talk more about this or if you have any other questions, it costs you nothing to click reply.