First of all, before going out to the gym, you should spend a lot of time on how to wear what kind of clothes, shoes and hairstyle. First impressions are very important. Make a good impression, and your road to picking up girls will be much easier. If you leave a bad impression on your sister, it will be difficult for you to attract her.
Secondly, when you are in the gym, you should pay attention to showing your good figure to girls. Most girls like boys with good figure. Many stars have so many female fans because they have enviable bodies. Therefore, if you show your good figure, it will increase the probability that your sister will pay attention to you.
There is also to think about the topic of communication with girls, and to talk about topics that girls like, such as celebrity shopping, rather than topics that girls don't like. Girls tend to like men who can talk. On the contrary, if you say nothing, even if you are handsome, girls will not be interested in you. But if you can chat, even if you look average, you are very attractive in the eyes of girls, so chatting is very important.
Finally, be considerate, give more help to your sisters, give them some guidance, teach them how to do sports well, give them some encouragement, give them water when they are thirsty, and do these things well, which will make girls look at you with new eyes. I think you are a considerate and reliable person. Pick up hot chicks is not difficult as long as you put your heart into it.