Any tips to help me sort this? A year ago I adopted a cat which is 2 years older than my resident cat. It took him a while to get used to his new home. Now the cats seem to compete with each other for my attention. They get along well as long as it's not a matter of being around me and my room. When they are both around me I give them affection equally. The problems begin when I sleep. They will yowl loudly for almost the entire night trying to get into my room or at each other. They'll yowl even if I lock them in different rooms. It feels like I'm their property. Is there a way to show them I love them both? Once they ended up attacking each other but fortunately now it's just hissing and show and they seem okay with each other unless I'm involved. Is this cat jealousy? They are both neutered.

Two of my 3 cats used to be the same. Looking back, I realized I did NOT give them enough attention. I should have played with them more and I'm pretty sure they would have felt more balanced.
I have several suggestions. First you can get some Feliway plug ins and put them in several rooms. It's a natural pheremone that calms them, perfectly safe. You can also get the Feliway spray, spray it on their beds, around the areas they hang out etc. NEVER spray it on the cat itself, and make sure it's dry before they lay on it. Also, try and get them plenty of things to distract them. Do they have any climbing towers or cat trees? Cats need to be up high to feel like they have control over their own situations. Do they have toys? Are you playing with them enough? What about getting walking harnesses and taking them outside to walk it off a little without letting them roam free? There's a lot you can do.
 Punkybrewster's reply was promoted to an answer.