В чем разница между him, his; its, it; their,them? Как правильно: 1.Lavrov comes to (his,him) office at 9 o'clock in the…

В чем разница между him, his; its, it; their,them? Как правильно: 1.Lavrov comes to (his,him) office at 9 o'clock in the morning.2.Our businessmens learn English. They want to speak (its, it) well.3.Our office manager often meets foreign bisinessmen and discusses prices for different goods with (their, them)?