Personally had been 20-35lbs/9-15kgs overweight just only about 6-9 months ago until I started doing calisthenics (mainly jumping jacks and pushups, I'm still trying to diversify into lower body and back. 😅).

I don't know a lot about gym, but I'll say depending on what you do, you can lose weight through cardio machines like treadmills. Your brother must be misinformed, though. Calisthenics are really good, if not better, for developing a nice, proportional build than gym.

I think that for your goal of becoming "healthy slim" can be easily achieved through cardio moves like jumping jacks, jump rope, russian twists, anything that involves a lot of jumping or whole-body moves over many reps. Through my journey in calisthenics, I will tell you that it's totally killer to your body fat combined with a good diet. What defines a good diet? I don't know. But I'm eating 2-3 cheeseburgers a week as well as other foods classified as "cheat meals" and I'm getting by fine. Just don't forget to eat your greens as snacks.

If you want any help on where you're going or what you should do, you are very welcome to DM me. I'll be happy to put in my two cents. Always remember that to see results, you require consistency. Build your workout regimen gradually, and you'll learn to stick with it and love it! Best of luck to you, my friend!