I want to fix these problems(according to my own opinion) which are having narrow/very slim arms and soft hips and thighs. I do different sports and think these problems are limiting me in some of them that I need stronger arms and surely having firmer hips and thighs can make me more beautiful and gives a better shape to my body. Which exercises do you suggest me for this reason? Please consider that I do not want to lose weight!
The number one workout you should absolutely be doing is the squat. It is bar-none the best functional exercise you can do, and it will work out your entire leg. A second workout to consider is the deadlift which is a good supplementary exercise alongside the squat.
As for arms, you're really going to want to target the triceps, shoulder, upper back, and chest to get a well-rounded and functional strength to apply in your sports. The bench press, the overhead press, and the bentover row will all build larger arms while also building necessary strength in the chest, shoulder, and back. Push ups, chin ups, pull ups, and handstands are all good body weight exercises that target these areas if you don't wish to involve barbells.
As for not losing weight, that is up to your diet. At its simplest, it comes down to calories in (consumed) versus calories out (burned). Figure out what your daily caloric intake needs to be to maintain your weight, factor in the calories burned from your sports and weightlifting, and you have your number of calories required to maintain your weight. However, I recommend eating 200-400 calories over maintenance to fuel muscle growth.