One thing that I am concerned about — how long ago was he neutered? He needs to be separated for at least a month or two from her (if she is unspayed) because he can still impregnate her if his hormones are still there.
The main thing with bonding is to ENSURE that all play dates end on a good note. The only way buns can bond is by figuring out what the hierarchy is between the buns you are bonding. They NEED to work this out to effectively bond. Having Play Dates before the surgery isn’t necessarily a bad thing but you have to work to ensure that each bond session ends on a GOOD note. Whether it’s simply you giving them treats with one on either side of you or they make a friendly little gesture towards each other. If they have been charging each other — maybe if one day they simply don’t charge each other… and sniff around each other — you can give them a few minutes and then put them away and do another bond session tomorrow. Most people choose to wait until after the surgery before attempting play dates and bonding but as someone who did most of the work before my trios surgery, it’s definitely not impossible if done in the right way.
The great thing about young buns — is they seem to be very accepting of other bunnies. Once they decide who the “top bun” is! One question, what exactly do you mean by charging? Do they run directly at each other and circle each other? Or do they charge and nip and bite? If they are not nipping and biting at each other that is a VERY good sign.