How To Get A Kitten To Calm Down?

I’ve had my kitten for about 6 months, but he’s always been a very nervous cat. He did get used to me after living with me for awhile because I would pet him and soothe him when he was stressed out, but it hasn’t really helped much. Now that his brother is here though, he doesn’t want to be around anyone or anything other than his brother at all times of the day. It drives me crazy! I’d like some advice on how to help calm down this boycat while still letting him know I’m there if needed while also not getting frustrated by the fact that this could take forever! Thank you in advance!!