In 90% of cases the male baby bunnies will start fighting if they came to puberty. They can be very aggressive and use their sharp teeth to hurt skin, ears and ballbag of each other. In the last case the injured rabbit can bleed to death.
Baby bunnies can be neutered before this point, so you avoid hurts and the need to separate them.
If you wait until puberty/ until fighting, they can become aggressive in a way that they can not be socialized again after neutering, because of bad memories with each other.
If male rabbits were neutered before puberty, they don't have to be separated from females (only for rehabilitation after operation, not for "avoid breeding"). Also their "smell" is not changing, because they did not lost their "adult" hormones - they had none before, they have none after neutering. Because of that, they will be accepted by each other as before the neutering.
The best way I can imagine is to select two male (?) baby bunnies with an option to bring them back if they are females, take them to the vet for sex determination and make also a date for neutering.
This early neutering has to take place around the 12th week of life. For a rabbit experienced vet this is a small routine operation and he/she does not even need to open the abdominal wall.
You can find more about the early neutering of male rabbits on this site called kaninchenwiese ("rabbit meadow") in German.
Some parts of this website translated via google:
("Rammler" means male rabbit)
The early castration at the Rammler
If a rabbit-rammler is castrated before sexual maturity, then one
speaks of an early castration. Depending on the size of the rabbits,
this must be done with about 11-12 weeks, but no later than 16 weeks
(larger breeds). In the rabbit usually the Rammler is castrated to
avoid offspring, since it is a smaller intervention in him than in the
females. The early intervention prevents sex hormones from being
produced, thus the rabbit never fully "grows up", but experience shows
that early neutered bullies do not have disadvantages in the group and
in rankings and are better socialized as they are not separated need
to be in order to prevent offspring. This is the great advantage of
early castration. If a Rammler is castrated before he is sexually
mature, he can directly back into the old group and grow up there.
Later castrated ramblers are capable of reproduction for up to four
weeks after castration and must be separated this time to avoid
offspring.
The Rammler castration after sexual maturity
Castration after sexual maturity can be carried out into old age as
long as the affected rabbit is vital and healthy. However, since the
sex behavior has an influence on the position in the group and the
whole character of the rabbit, especially in older, dominant rabbits,
which live in a group, after castration, there may be a loss of
ranking, which often makes them emotionally strong, especially in
group housing added. Rabbits are very much designed to reproduce, so
the sudden loss of affected hormones often results in a character
change. Since in captivity, however, no natural selection (by
predators and disease) takes place, we have no choice but to castrate
them, because a single husbandry or permanent offspring would not be
animal-friendly.
Rabbits are fertile for a while after castration! The separation of
the Rammlers of sexually mature females after castration must be
strictly adhered to, as there is still a residue of sperm in the vas
deferens, which can still be delivered. Only when these residual sperm
have died, the rabbit is no longer able to produce. How long the
remaining sperm are still viable, is not scientifically researched,
the guinea pig, there is a study that has found out 7-70 days, the
same is probably true for rabbits. That would mean that (to exclude
any risk of danger) you would have to wait 10 weeks for quarantine. In
practice, however, it has been found that a shorter period is
sufficient. After 4 weeks, only extremely rare cases have become known
in which there was still a pregnancy, after 5 weeks separation, there
has been no single pregnancy. The first four weeks are dangerous. The
only exception: if the ram was castrated before it became sexually
mature (early castration), there are still no sperm present in the vas
deferens, i. the castrate can be left to females directly after the
castration.
