I know it's not acceptable to share games, but my brother had got playstation plus and downloaded some games for vita on the ps3. The thing is it's on his account and my vita is linked to my psn account instead of his. Is there some type of way to link those two accounts instead of paying for two playstation plus accounts on one console?
No. To play the games on his account, your Vita needs to be exclusively linked to his account. As of right now there is no merging of any accounts whatsoever. Not even the competition will entertain this notion since they want your money. In other words, if you want those games on your account you must buy them with your account
But, if you have an extra memory card, you can set one up for your account and one for his. You will just need to restore the Vita when switching accounts, then you can play your games and his games.