A multi-cat household can be tricky. Typically siblings are preferred as they have grown up accepting the scent of the other cat. Introducing a second cat into a home where a single cat has had time to claim the territory can take some time and patience.
Some cats will willingly accept a second cat, others will not. Even siblings can be hit and miss.
Normally two females are better than two males, as the males tend to want to establish Alpha leaving one to be dominated. One male and one female, as long they are neutered can work well as the different sexes have unique rolls in a clowder.
Cats will clean each other in a futile attempt to eradicate the scent of the other animal from the home. Usually they need their own litter box, but sometimes they will share. Again, the scent thing.
Overall, indoor cats do better with another cat around. It gives them another animal to practice their hunting skills with and to keep physically fit. If a single cat has already formed a bond with a human, there can be jealousy if the new cat gets attention as it taints the marking from the original cat. Just have to watch how everyone interacts.
On the subject of maintaining weight, many breeds will self-maintain their weight, while others have to have food metered to them. If you find you have a mix between the two, you have to watch them eat or the one who is not maintaining weight will eat the other cats food. We have that situation with our two. They are siblings, but she is a tubby thing, while he is lean and mean. He will also leave his food for her to eat. It is a pain in the tush at feeding time.
Speaking of food. The cat food industry is a despicable industry. They do not hesitate to include ingredients known to be bad for cats. Two in particular are widely used and should be avoided for the long term health of the cat. Guar gum and carrageenan are both used as gelling ingredients in many foods.
Unfortunately, guar gum inhibits protein absorption in a cat. Cats need a lot of protein for all thier organs and to maintain muscle mass. Carrageenan is a known carcinogen to cats.
Hard food, in general, is not a good food for a cat either. Think about how cats live in the wild. They eat fresh kills. Cats do not drink a lot of water as they get most of their moisture from the blood of their kills. Cats also need taurine to maintain their eyes. Taurine is found in fresh red meat, poultry, eggs, some dairy, and shellfish. However, when any of that is processed into hard food it destroys the natural taurine. That is why you see taurine added as an ingredient.
I learned all this when I lost a cat to CRF (chronic renal failure). Turns out the food we fed her brought it on. If you Vet recommends hard food for a cat, then that Vet has been bought and paid for by the cat food industry. It is a slimy industry. There are many Vets who do not like cats. Just beware of that.
It has gotten so bad here, a new market has opened up for Vets who only treat cats and that is it.
Ok, I'll get off my soapbox now.
