所有的人 means all the people.i think it is like 'everyone' in English.For example,the teacher sometimes use it in class.所有人的一起读(everyone read this together.)
其他人 means other people,we use it after you already have said someone,For example,在教室里,我在读书,其他人在做作业。(In the classroom,i am reading books,other people are doing their homework.)or we can say,我和你去购物,其他人可以回家了。(You and i go to shopping,and other people can go home.)I think另外的人 is so close to 其他人,i use both of them at some situation.I can't tell their differences even if i am a native speaker.Haha.