Is playing cat sounds bad for my cat, or does it mean he's lonely?

Thanks for using Petco Pet Education Center, formerly Petcoach! I would not be alarmed by this at all. The beauty of cats is how particular and unique they are and some cats just like to keep to their own more. You may get another cat for sure though this is not necessary. Best of luck!

It certainly may help! Just like people, some cats are more social than others. If you decide to get her a playmate, try to find a cat with a similiar, playful temperament and about her same age (that way the energy level is matched). Ideally get a cat who is coming from a living arrangement with other cats so that it is already use to living with other felines. Expect that there may be some hissing or unease for the first couple weeks. It’s very normal for this behavior in the beginning and does not mean they won’t like each other. I hope this is helpful and please feel free to post any additional questions!

If Wilkie was used to having a friend, it might help to get him another. However, I noticed you marked him as unneutered, and it could be that there is a female in heat nearby attracting him, which in turn makes him want to stay outside/causes his increased vocalization. Sometimes, neutering can help and may keep him closer to home and out of trouble. Ruling out any illnesses is also a good idea, especially if he seems confused, hurt, or painful when he's indoors or around you.

That is very cute! Some cats like the sound of their own voice, or she may be making the noise to get your attention to you to play with her and her favorite toy. As long as she is eating and drinking normally, using the litter box normally, and behaving normally, I would view this as a cute little quirk of hers and I would not worry about it :-)

I would first recommend taking Marley to the vet make sure he is healthy. Some cats will become more affectionate when they are sick or not feel well. Second I would recommend increasing toy and activity in the house. He could be getting bored so he is trying to play/interact with you more. They do make toys that can hide treats in them. You can try and hid toys around the house so he has to go find them. Increasing his activity will really help in this situation

He is adorable! This sounds like a behavioral issue. . I know you said you give him a lot of attention and play time but you may need to do some "environmental enrichment" as well (see links below). And if Feliway is available in your country you should definitely get some diffusers for your house. ( https://shop.vivapets.com/il/feliway-classic-diffuser-refill-48-ml-1-unity ) ( thedrakecenter.com/materials/environmental-enrichment-indoor-cats ) ( https://www.youtube.com/watch?v=AejmrLa_Cs4 )

There are these amazing toys by Catit such as the senses play circuit. It's a ball on a track that cats can chase around and around on their own. They have a whole series of toys designed for solitary play, so check it out online. These may be suitable for Leo. I hope this helps!