Tries to play it cool: Diluc, Scaramouche
Diluc is so embarrassed. Though he's mostly able to stay composed, coming up with a somewhat believable lie, his bright red face gives him away. Hopefully you're too caught up petting the cutie to notice.
Scaramouche storms over, demanding to know what the hell you think you're doing, when he stops in his tracks. Oh. You were talking to an animal. Look, he wasn't jealous okay? He was just, um, whatever! It's none of your business, just get back inside.
Neither confirms nor denies: Albedo, Kaeya
Albedo calms down tremendously after seeing the animal. If you're paying attention, you might even see him visibly relax. Should you question why he came over, he'll say he came to check on things. If you connect the dots and press further, asking if he was jealous, his silence will tell you everything you need to know.
Kaeya is, admittedly, a little embarrassed at the misunderstanding. Still, animal or not, he isn't pleased you're giving affection to someone other than him. He'll sling an arm around your shoulders, muttering something about how it's time to go. Any raised questions will simply be deflected or brushed aside.
Shamelessly admits to being jealous: Childe. Kazuha
Childe both does and doesn't care what you think. He wants you to think highly of him, of course, but your opinion doesn't change anything. Not when he's so much stronger than you. At the end of the day, he does what he wants, but at least he's honest about it.
Kazuha doesn't see the problem with being jealous. To him, jealousy is just a testament to how much he adores you. The amount of jealousy, who or what it's directed at, doesn't matter. It's perfectly normal, so there's no issue, right?