Well, if your mom cannot take them back, I'm sure you could place them with a Chihuahua rescue easily. They're adorable and its very easy to find homes for small dogs.

Maybe it'd be easier to try to paper train them or litter train them. I don't generally recommend it unless someone wants to use that method for the rest of the dog's life, but it may be easier in your situation. The Chis got used to going all over the floor, whereas most puppies are conditioned to potty on grass from a young age. You just need to change the texture/surface that they are used to going potty on. I'd cover the dog crate with newspaper and keep them in there until they go. Then praise them whenever they do go on the paper. You can try putting spots of newspaper all over your floor too in whichever room they stay in. So if they're about to have an accident, they'll see the newspaper and maybe go there. Eventually you will be able to take most of the paper away and try to leave them one good spot of newspaper. I know it'll be messy and more cleaning for you, and probably not be good with the house on the market. Just a suggestion though.