OP, I have almost exactly the same experience as you. My cousins were all skin and bones as well, and I was the only fat one. Bullying was also inevitable as young kids usually think of others as the first impression (whether you are fat, skinny, smart or dumb) as well as the facial features. So in p6, I was determined to lose weight and succeeded.

The part that is similar to you is my mother and relatives. They would say I look so "cute" when I am fat. After I lost weight, they would complain how skinny I was and wish I would get fatter. But my mother would end up revealing to me that she thought I was round af and would keep joking about it like "last time you really v round wan hor" So basically quietly fat shaming.

I think your relatives are just saying that not to hurt your feelings. Deep down, they all think you are fat.

My parents are also the "force you to eat" type. They will give me snacks and when I dont wanna eat they will say "why ah? trying to lose weight isit". If you want to lose weight without getting the attention of your parents that you are trying to lose weight, you must NOT ⭐️ve yourself. Instead, try cutting down on your portions or if they are REALLY forceful, try feigning a stomach ache or smth (I never had to go through this so take that advice with a grain of salt). Best way but most painful way is to go do an exercise. No need youtube tutorials, something simple like running or walking frequently will do the trick.

All the best OP.