I think your aunt and uncle are asking you to socialize with your guests. Sweety, you're going to need to do that even if you don't really feel like it. You can just say hi and sit for a few minutes and ask for their excuse to leave them alone. You don't have to change your personality, but you need to start practising socializing. I understand that you live in USA, but your family still have their social habits that they still practise, so you need to be in between. I think this will solve your problem with your uncle and aunt and believe me it's going to help you later on when you get married because if you get used to socializing, you will make less effort to deal with your in laws. When you get married insha^Allah, you will have to change some of your habits that you never thought you would change. Why? because you will be two persons making one decision at quite a few times, and in order to reach one decision one has to sacrifice what he / she wants in order to satisfy who he/she loves. Sometimes, you don't feel like seeing anyone, but you still have to go with your husband to visit your in laws...You still have to accept a dinner invitation by your in laws...When you get married, you do get some freedom, and at the same time, you lose some of your self freedom by having to do what others want.
On the other hand, if you feel comfortable being skinny. Then, don't listen to them. As for not speaking a lot, this is a good quality that you need to keep, and I advise you to stick to it, but what you can do is to distribute smiles whenever possible to compensate for not speaking if they're going to be too hard on you.
If you're having difficulty living with them, you will need to try another approach which is to try to be nice as much as you can. You don't have to talk a lot as they want you to, but keep smiling at them whenever possible to have a warm atmosphere. I know it's not an easy situation, but you need to make less stressful than what it is for yourself.
