Mice vs. Rats (again)

[Bighead]

I have a few questions. I have 3 corn snakes that are roughly 20, 25, and 30 grams and a bal python that is 900 grams. I bought a pair of mice to breed for the corns, but they stopped after 2 litters. I'm guessing one of them is too old or something. Anyway, I just bought a pair of rats to breed for the python. How much do pinky rats weigh? Do you think I could feed them to my corns? I have also never fed my python rats before. What size (by weight and/or "stage" should I try feeding him? He eat's 3 adult mice per week right now.

Just so you know, I have only had him 3 weeks and this is what the previous owner was feeding him. He is also over 3 years old. Is this on the small side for a bp this old or is it ok?

Thanks.