Yes, you do need to keep them completely separate for another 1-2 months. Your bunnies aren’t bonded. Being from the same litter has no affect on bonding. They got along fine as babies, as most buns do, but once hitting puberty everything can change. I’m suspecting it happened now because one of your buns is going through a post neuter craze, which will get worse before it gets better. Your buns are adapting to the hormone changes. They need to be completely separated at all times (including playtime) while you do prebonding. So you need to change their litters between the cages and different items within their cages, as well as swapping them between cages every few days. Do this for the next 1-2 months. Afterwards you will need to begin bonding them in a neutral territory. There’s more about all this in the bonding forum.
As a side note, check Opal’s neuter site. For 1-2 weeks after a neuter a buns exercise should be limited so the site won’t open or become infected. If there was any kind of chasing, nipping, fighting, etc then you need to make sure he wasn’t hurt down there.