I've always loved what my now deceased ex-husband used to say when he said you never truly know a person until you know their boundaries. And, you can't truly love a person until or unless you know them. Your parents don't seem to have a problem making their boundaries known, it's time you begin to let them know where yours are.
Being that your kitten is yours, you can tell them you will not have your kitten declawed. Tell them this and tell them all the reasons morally and ethically why you cannot do this to another living thing. If they don't respect your wishes, they can choose to "cut you off" but they won't. Believe me, they want you to go to college a whole hell of a lot more than they want your kitten declawed. Think about it.
Every time they bring it up after your initial boundary discussion just *calmly* tell them, "I've already discussed this with you, what more do you want to know?
Then when they persist, tell them, "I will be devastated if I cannot go to college, but I will be more devastated to knowingly harm a kitten I know I can train to refrain from scratching over time." Tell them you cannot get financial aid grants and loans either and working yourself will not cover the cost of a degree, so you'll be forced to work at McDonalds. Don't freak out when they say, "Okay, I guess you'll be working at McDonalds then." Just go fill out the application.
Eventually you will no longer be under their wing, so to speak, and then you WILL be able to get both grants and loans via the federal government, and you deserve these. By the way, everyone deserves love and respect, both.
If they continue arguing with you, just say, "I've nothing left to say. I'm really sorry you are forcing this on me, I wish it weren't so but I feel strongly about declawing."
If I am wrong, and after a month or so of you sticking to this routine with them, if they really aren't going to pay for your college over a kitten, then ask your parents if your giving the kitten away will be an acceptable compromise. Tell them that shelters often find homes for unwanted pets but do not say exactly how you plan on getting rid of the kitten. If this will make your parents happy, give the kitten to a close friend to hold for you--but do not tell your parents anything except that you gave the kitten away, end of story.
Do not speak of it again with them. Learn to change the subject graciously. Practice practice practice. It's a skill you'll be needing.
Have the friend give the kitten back once you are firmly ensconced in college. In this way you are not lying.
You need to start laying out these type of boundaries with your parents anyway, given they're being so unreasonable. Always be very clear, and never talk about things beyond what is required to be clear--don't go into too many details. This is how pulling back works with controlling parents--you're essentially training them....
However, I strongly suggest you might want to get the support of a good counselor and work with him/her on this parents problem. That type of work will pay off big time in the long run, believe me. It's not going to be easy, so you might as well get someone who is on your side for support. Many people use counselors in this way, they go for the express purpose of working on a specific relationship, or parents, or even any life change (like going to college) and when they are done, it is agreed the therapy ends. All universities have counselors who are usually both good and cheap if not free. In the meantime, see if you can get someone locally to help you with this.
Keep us posted too, I hope.