Can they legally keep my cat?

From what you have said, it seems like they really are just joking. My suggestion is to proceed as if they are really just kidding. If they are, then you avoid a lot of awkwardness. If they are not, then you will find out anyway and will the force of your will might even just convince them to give in.

Make a plan of some days and times when you could go pick your cat and her stuff up from them, and then ask them which time would be best for them. Give them three options, spaced out over a week, and be firm about it. Saying "When would it be convenient for me to come pick up the cat and her things? I was thinking ______, _______, or ________. Which would be best for you?" is clear and straightforward. If they don't respond or try to push it off, ask your girlfriend to get involved and nudge them about it.

yes

Just pick up your cat when you're there and walk out with her. They are out of line. It's YOUR cat and if you take it there is nothing they can do.

When we first got our cat to a vet he received a passport where they put all vaccinations and if i want to take him abroad i take it with me, there it stands i am the owner, so if i and my husband get a divorce my cat belongs to me with no dispute. Shouldnt u have such a passport if your cat was to a vet? How else anyone would know what sort of vaccination the cat had?

Oh please. You claim you've paid for all the food and supplies for this cat? For how long? And you stop by DAILY to scoop its litter and change it every week?

You're a liar. You dumped this cat on your girlfriend's family and THEY have provided for it all this time. It's not your cat anymore. Such a liar there's "mold" in the cat box.

They could try, but they probably won't. Legally, if you have been paying for the cat's vet bills, and even food, and it was previously agreed that the arrangement was temporary, they have absolutely no legal right to the cat, especially if they are not providing the standard of care expected. It was clearly still your cat if you have been providing for the cat, and there was a verbal agreement that the cat would be returned. Even if that wasn't the case, if they are neglecting the cat.

I'm sure they were just kidding though. When it's time for the cat to come back, if they won't relinquish him/her, your best bet is to take the cat anyway. If they refuse, go over and visit, and pick the cat up and leave. Use your gf's key to go in when they aren't home and take the cat. It is your cat, so you cannot get in trouble, and then if it did go to court, you wouldn't have to wait to get your cat back. Do this before taking legal action.

Anyway, surely they are just being social and kidding, and even if they weren't, the cat is absolutely legally yours, you just don't want to have to wait if they are nuts.

Appologize for kitty being there so long. Offer (you will have with you and really mean they can have) some more money to cover their time and effort; hand it over.

Tell them if they want to share the cat, they can, but for now you need kitty with you because you really miss her.

Appologize again.

Scoop her up and put her in the carrier u have night in with you. Tell them they can stay come and visit the cat. Leave when kitty, offering hugs, if they are that sort of people.

The cat is your property. You may call the police and begin legal procedings against mother.

Ask them if they'd like a cat of their own and refer them to an animal shelter you've looked into. If they still say 'no' do what Laura suggested.

If you support the cat financially, then the cat is legally yours.

They can try to take you to court, but you can prove that you have been providing her care.

The next time you go over there to feed her, just pick her up and walk out. If they want to call the cops or make a scene, let them. its your cat.