You should be able to, to a degree.

Did you notice they got messier when they reached 3-4 months old?

How have you set up their habitat? Do they have a cage, pen, other? Do you use paper or wood bedding? Do you have a large litterbox they both can be in at the same time?
Do you place hay in the litterbox on in a rack over the box?

One other question, are you 100% certain they are both boys? 

Yes you can. I think a good amount of rabbits, including Wick, have been litter trained without having been neutered. Wick is about 6mo and is litter trained. It took a while, but now if he’s left alone for multiple hours, I come home and find no outlier poops or pees. If anything, he does those when someone’s home, in a sassy reaction to something we’ve done.

Posted By Catalin on 5/21/2017 11:27 AM

I just bought a small litter and some paper-based bedding. They live in an outside cage during spring and summer, and during fall and winter the will stay in a pen in our apartament. Neither me nor their vet are 100% sure if they’re males, but I assume they are because they, well “ride” each other. Luckily, they have a vet visit this month, and, since they grew up, we can check for sure. I want to give the litter to my grandma tommorow, so she can intall it with hay and bedding, but if you think I should buy a bigger one, I will try to return it to the pet store

You could stop using the paper bedding, I think that might help. Rabbits often like to lie on surfaces clear of bedding anyway and they wouldn’t need it for warmth. When using bedding and litter, they don’t always see them as different, so they’ll just use the bedding as litter. 

They would be quite hormonal though and marking with poop and urine, so litter training could be a challenge seeing as there are 2 rabbits. 

At their age, you will really need to determine their gender for certain. If you do have a male and female, you’re going to get babies before too long.

  Are any testicles obvious?  Rabbits can pull them back up so no testicles doesn;t necessarily mean they aren’t males. It just means they may not have descended yet or the rabbit has pulled then back up. 

Mounting behaviour is not specific for gender either. Females will hump males and other females. When they rabbits are doing this, if you pull the mounting bun off. you can sometimes see it is obviously a boy.   But again, not seeing anything automatically makes the bun a girl either.