Oopsie, there is a way to get both Coco and Patches to max hearts but it's actually incredibly difficult (I'm going to release an update that'll make it easier).
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For Coco, there are two +1 heart interactions in the kitchen and one in the bathroom (so you can just skip that part where you ask Angel about Patches). It's difficult cuz there's a bug that only allows you to get the +1 heart for Coco if you interacted with the knives in the kitchen in Chapter 1! >O< As for Patches you can max him out in purrgatory. :3
If you play again, wait for the update that'll be out in a day or two >:3 There'll be a small bonus for completing the best ending while having everyone at maximum hearts. ALSOO thanks so much for playing and everything ;w; !!