Impressive interpretation! :D Daughters are affectionately called बेटा all the time. However, this usage is restricted solely to a situation where one is addressing the daughter. बेटा in such assertive sentences only holds the meaning of a 'son'. So, if you wish to say 'He has seven children', you would say 'उसके सात बच्चे हैं", बच्चे meaning children.
so is the पास not always required to indicate possession? I read this as "his seven sons", compared with the entry उसके पास कई कुत्ते हैं translated as "she has many dogs"
This is one of those odd things that most languages have. You just have to learn how it works.
Yes, you're partially right.
The phrase "उसके सात बेटे" would mean His seven sons but as soon as you add the है at the end, it becomes a complete sentence and its meaning changes to He has seven sons.
But if you say -
उसके सात बेटे दिल्ली गए - His seven sons went to Delhi.
So the phrase preserves its meaning in some instances.