"I have to study but Aamir has to play."
Translation:मुझे पढ़ना है लेकिन आमिर को खेलना है।
Where would you put the other को?
If it's in 'I have to study', then note that मुझे can be understood to be 'मैं'+ 'को'.
To elaborate, postpositions in Hindi typically only accompany nouns. Pronouns have a case-system instead where their form is changed. A lot of the times, it is pretty evident (For example, 'आपको' is the dative-case form of आप which would be equivalent to adding the postposition को) but not always.
This construction in Hindi can mean either 'want to' or 'have to' so you can as well translate it as 'I have to study but Aamir wants to play' or 'I want to study but Aamir wants to play'. Which of these meanings is intended can be figured out through the context.
But if Aamir is a professional athlete or a kid in a school with mandatory PE classes, maybe its 'Aamir has to play' after all.