Hell Lc23.
This is such a sad situation you're in , in many respects, although obviously exciting that you're expecting a new addition to your family.
It's commendable that you're looking to re-home your two babies together, and clearly a foster position would be ideal for you, albeit possibly a more difficult outcome to obtain.
It might help with the process if you can give us a little more information. What area do you live in, and are you able to post photos of the cats? Are they indoor only cats, and have they been neutered and vaccinated?