First of all, I wanted to say I'm sorry for your loss. I could not imagine losing my baby.
I do not have experience with two, but I have read a lot. I have read (like you said) having the opposite sex is the best. I would suggest spaying and neutering them both... even after your experience. I would suggest waiting until they weigh about 4-5 pounds, so they have a better chance and are stronger.
There are so many benefits to spaying and neutering... If you spay your girl, it gives her such a better chance of not getting cancer. The male- it will help with his behaviors (humping, marking, etc).
I really hope that you can find your babies as soon as you are ready
I'm sure others will have more advice for you because they have experience.
Good luck!