Talk to your family. How long do they want to wait?
Adopting an animal is a commitment, and you seem ready to make that.
This.
It seems like it’s too early for them to get another cat. No point in trying to rationalise it, or saying who is wrong and who is right. Their grief seems to look a bit different than yours, that is ok, and neither is wrong.
This is the time for a honest conversation, asking when they thing they might be ready, and not having any sort of expectations.
Trying to force an ok right now might lead to resentment towards the cat in the future, which would not be fair for the cat.
You had mentioned that Moses was your brother’s cat, so the final decision lies with him. If the new cat continues to be a family pet, then there is not much you can do until he feels ready.
At the same time, as Sally says, that does not mean that you aren’t capable of taking on a cat. You have the experience, and if you’re in a financial position to do so, then I don’t see a problem with you getting one. I just wouldn’t expect your family to care care of the new cat or anything
