Toddler and an infant, mixing diapers?

Hello all!

I was wondering, in a few short months I will have a 2 year old boy and an infant girl in diapers. I have mostly Bumgenius and Thirsties, pocket and AIOs.

Can I mix diapers between the babies or do I need to have diapers for the toddler only?

Is there a way I should wash them to make sure they're clean enough for either to use?

Thank you in advance!!!