Ludzie is a masculine personal noun, you use masculine personal forms, which usually end in -i, sometimes -y.
I would add "Ci ludzie" as well. (I'm polish and taking the exam for fun lmao) "Ci" is just a shorter form of "Tamci".
You may be right. I never really thought about this. But many people use "ci" and "tamci" interchangeably. Maybe it's a mistake on our side.
It's wrong. I cannot give you exact rule, but "tamte" is used for non personal "tamte drzewa" or feminine "tamte dziewczyny". https://en.wiktionary.org/wiki/Appendix:Polish_pronouns#Demonstrative_pronouns:_ten.2C_tamten
Ten zwrot przypomina mnie o piosence Anny Jantar: gdzie są dzisiaj tamci ludzie :) Jak widzę ten zwrot, myślę o tamtej piosence. :)
In the same way as ten (this, that) and tamten (that). Ci can be these or those depending on situation and context. Tamci is always those.