does 'Los estudiantes' go with 'estudian' or 'estudiamos'?
The subject, estudiantes, can be replaced with the subject pronoun ellos (they) so that is the correct verb form.
Estudiamos should only be used to say "we study".
Since it is los estudiantes is in the plural form, representing "they" it would be estudian not estudiamos(for we)
If I'm one of the students I would say "estudiamos". From the looks of this sentence, I would guess that we're talking about a group that does not include me--so "estudian".
"Como estudiantes, estudiamos español todos los días."
"Aquellos estudiantes estudian español todos los días."