Learn Farsi: نوجوان توقع دارد والدین به او اجازه دهند معاشرت کند. - The teenager expects the parents to permit him to socialize.

This sentence has a chain of dependencies. The first verb, توقع دارد (expects), requires the next verb to be in the subjunctive: that they permit (اجازه دهند). Then, this verb of permission also requires a subjunctive for the action being permitted: that he socialize (معاشرت کند). This creates a chain of subjunctives.

I thought subjunctive verbs usually start with the prefix بـ (be-). Why don't دهند and کند have it?

That is a great observation! Both اجازه دادن (to permit) and معاشرت کردن (to socialize) are compound verbs. For compound verbs made with دادن (dâdan) and کردن (kardan), it is standard to drop the بـ (be-) prefix in the subjunctive. You simply use the present stem of the light verb plus the personal ending.

Why does the sentence use به او (to him) instead of a direct object like او را (u râ)?

The verb اجازه دادن literally translates to "to give permission." Just like you give a physical object to someone, in Farsi the person receiving the permission is an indirect object marked with the preposition به (to).

The word for parents is والدین (vâledeyn). What kind of plural ending is '-eyn'?

والدین is a word borrowed directly from Arabic. The '-eyn' suffix is an Arabic "dual" ending, meaning exactly two of something. Farsi adopted this specific form to mean "parents" (the two parents). Because it refers to more than one person, it correctly takes the plural verb form in .