Their styles differ.

[WilliamTaft]

An example sentence using "differ" in The Britannica Dictionary: Their styles differ.

Does "their" refer to two people?

 

[Tarheel]

Probably.

 

[jutfrank]

Without context we don't know who or how many people the reference word their refers to. Logically, we know only that it is at least two.

 

[Tarheel]

I said "Probably" because" that's what would I expect from experience. Of course, without context you can't be sure.