一会儿就。。。。In a moment, [*] will.... 马上就。。。了 Immediately [*] shall 马上要。。。了 Immediately [*] must/will/have to/ [*] a pronoun of he/she/it/they depending on the context.

Yes, they all refer to "will happen very soon". 一会儿就 more like “in a moment”；马上 more like“right away”. In most conditions， 马上就=马上就要=马上要 马上就到了=马上就要到了=马上要到了=马上到了 马上就好了=马上就要好了=马上好了 However ，we don't normally say 马上要好了

一会儿就到 马上就到了 马上要到了 can really just express the same idea “someone is almost somewhere”

yes, you are right. They all can express the same meaning. For example: Chris， 一会儿就要上课了。 Chris, we are going to have classes now. Chris，马上就可以吃饭了。 Chris, your meal is ready. / Chris, you can have your meal whenever you want. Chris，马上要结束了。 Chris, it is going to be finished very soon.

Hi, the first one is too vage to discuss here. 马上就。。。了 It's use like this: I 马上就 finish home work 了. The home work is finised, because of you. 马上要。。。了 the sky 马上要rain了。So it's going to rain. You can't rain. So you use 要 here。 example, you and your wife are going to take a train. But your wife is doing makeup. So you would say Hury, it will be late. 马上要晚点了。 she would say, I almost finish it. 马上就好了。