Each of the sons followed ___ father's advice.

The traditional rule holds that the subject of a sentence beginning with each is grammatically singular, and the verb and following pronouns must be singular.
Thus you should say, “Each of the apartments has (not have) its (not their) own private entrance (not entrances)”.

তাই singular pronoun হিসেবে এখানে his বসবে।

Source: Cliffs Toefl