This parable is also referenced in my Bible in Mark 13:33-37 as being similar in structure.
"Take heed, watch and pray; for you do not know when the time is. It is like a man going to a far country, who left his house and gave authority to his servants, and to each his work, and commanded the doorkeeper to watch. Watchtherefore, for you do not know when the master of the house is coming-in the eveneing, at midnight, at the crowing of the rooster, or in the morning- lest coming suddenly, he finds you sleeping. And what I say to you , I say to all; Watch."
If I remember correctly the Watchtower understanding on this is the possessive pronoun, his, refers to the Master. They also refer to themselves as the wise slave recorded in Matthew 25:45-47, therefore they consider possessing authority over the belongings.
Sidenote:
The exegesis of Mathew 25:45-47 in my opinion is not too far off from what Watchtower teaches. In my church, the Scripture concerning the wise servants refers to the hierarchy of the church; namely the deacons, priests, bishops etc. The difference between WT theology and Christian theology on these verses is a matter of what kind of relationship does the stewart have with the domestics. In Watchtower theology it is an authoritarian control over the domestics. In Christian theology the stewarts, being leaders in the Churches, work more as caretakers and not rulers.
Peace
Maksym