This post isn’t so much a litter training post as one about bonding, so you might want to change the title to get more help, and maybe the moderators can move it to the bonding section.
First, they need more time for their hormones to settle.
Once this happens, you need to properly bond them after a pre-bonding period. This means cage swaps for 3-4 weeks until the don’t show territorial behavior towards each other when you swap cages.
They should not have any play dates together, as they are obviously not bonded (chasing and humping are both dominance displays).
Once their hormones are more settled and you’ve done pre-bonding, you can do supervised dates in neutral space. The space you use is very important, it must be some place that neither rabbit has been before.
I recommend reading some bonding journals to get a better sense of the process.
Litter habits should return once they are bonded, but will probably continue to be bad until that happens.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.