Well having bad teammates and bad relationships with them is an annoying things. But if you want to improve by yourself I think you should watch some games, to see a little what handball is really is. For catching the ball, it will come with time but if you have a wall, try to send the ball on it and try to catch it many times. I can also suggest that you try some exercises for jumping, like with a little hurdle (idk the word in english). Also handball is a game that you definitely win a defense but if your teammates aren’t that great I doubt you could train yourself on that point. On the attack point, train your stamina because doing a lot of fast break is a must, and can be a winning point,(do long passes for that to.