You will need to keep your bunnies separated at this point. At their age, they are nearing or entering puberty and will be dealing with all the hormones that brings. Besides humping, they may very well start fighting. Rabbits can severely injure each other when they fight. And if they do fight, they likely will not want to be together in the future. Rabbits can hold a grudge. It doesn’t matter if they’ve been living together and getting along up to now, when you start dealing with hormones, everything changes. And are you absolutely sure that they are both females? Many people have been told that, then they end up with an unexpected litter.
Keep your bunnies separated at all times, they shouldn’t even be let out together for a few minutes of play. They will be old enough to be spayed in 2 or 3 months. After their surgeries, you should wait a month or so for the hormones to abate, then you start bonding procedures.
Here are 2 good articles on bonding:
https://rabbit.org/faq-bonding-multiple-rabbits/
https://binkybunny.com/BUNNYINFO/tabid/53/CategoryID/9/PID/940/Default.aspx