He could just have a more cautious and standoffish personality or it could be due to hormones. You really don’t know what a bunny’s personality will be like until they are an adult and have been neutered.
The best thing to do is just spend time with them on the floor. Don’t try to force him to interact with you but let him approach you if he wishes too. Bunnies are curious animals and letting him dictate the pace will make him trust you faster and grow more comfortable in your presence.
Non-stop pooing sounds like marking. His hormones are coming in and he’s around another bunny. He needs to make sure everyone in the house understands what is his space. It’ll get better after he is neutered.

I have always had some success with “ignoring” my buns when they are shy at first. You can lay on the floor with a book or computer in their area and then simply ignore them. Another trick is to leave some treats leading from them up to you. You want them to associate you with good things – like treats! Bribery is not a crime when getting your bun to learn to trust you!

Lots of buns have lots of different personalities though and you may just end up with two with completely different likes and dislikes. I have five and believe me, they ALL let me know when I do something they don’t like (even if someone else does). Getting them neutered will help with some of those horrid behaviors such as leaving their pellets and urine all over the floor but don’t expect them to become litter trained until AFTER their neuter and the four-six week waiting period. Until then, litter training can be frustrating and just plain useless.

All buns act differently when they are hormonal as well. Two of my rabbits I never even could tell while my one was a complete disaster. Her hormones were on high impulse and she was just a horrid little thing to be around! LOL. You’ll just have to deal with the attitude and teenage brattiness until after their neuters! (If they become horrid like my Nora that is!)