I have to say I find it counterproductive that whole sentences are often glossed. Understanding that Ukrainian grammar and English grammar are different is part of the learning process. I would prefer having individual word glosses, and then it being up to the learner to piece together the meaning of the sentence. "Чиї" - whose (pl), це (this/these) студенти (students). It feels like cheating to mouse over one word and be given the exact answer.
[noticing that you are learning German as well] "це" is like "das" in German. Works both for singular (das ist) and plural (das sind). You can say "Wessen Eltern sind das?", right? So we just skip the "sind" and only leave "das" which does not indicate plural or singular.
Been awhile since I did any German, but that sounds like demonstratives in Dutch. Not sure about German, but in Dutch dat/dit (that/this) become die/deze for plurals depending on usage* ("this house"="dit huis" and "these houses"="deze huizen" but "this is a house"="dit is een huis" and "these are houses"="dit zijn huizen"). Is that (roughly) what's going on here with це/ці? "What is/are це?" but "Це student is..." and "Ці students are..."
*Gender also matters for which form is used in Dutch (and I believe German as well), but for the sake of simplicity I used a neuter word to avoid gender complicating the pattern.
Yes, it's similar to the example that you wrote with houses.
When you are talking about "this" as kind of an adjective it will be цей-ця-це-ці.
When you are talking about "this" as not modifying a noun but being the subject of a sentence, it will be just це*.
Detailed examples (sorry, couldn't make it shorter):
- Це does not carry a gender and does not indicate singular/plural (це = das = esto/este/ésta/estos).
[m] Це студент = This is a student = Das ist ein Student = Este es un estudiante.
[f] Це студентка = This is a student = Das ist eine Studentin = Ésta es una estudiante.
[pl] Це студенти = These are students = Das sind Studenten = Estos son estudiantes.
- Цей-ця-це-ці carry a gender (цей = dieser = este, ця = diese = esta, ...)
[m] Цей студент = This student = Dieser Student = Este estudiante.
[f] Ця студентка = This student = Diese Studentin = Esta estudiante.
[pl] Ці студенти = These students = Diese Studenten = Estos/estas estudiantes.
The confusion might arise with neutre
[n] Це село can mean both "this is a village" (Das ist ein Dorf) and "this village" (Dieses Dorf). Basically imagine German "Das ist Dorf" and "Das Dorf", we drop "ist" so it becomes messy :)
Sorry, I can't do Dutch, so you try to guess by my German :) * potato for a long post *