Hi All,
Pardon the noob question.
I am looking to book a round trip within a round trip. Is it called nested?
Basically i want to travel:

A to B, stay 3 days,
B to C stay 3 weeks,
C to B, stay 3 days,
B to A, go back to work.

Because of cost of stopover flight (travel for 4 people), i want to book on round trip A-B, and another round trip B-C within the time of the first one.
A-B...(B-C................C-B)...B-A

If it is not allowed, how do airlines detect and enforce it?

A thousand apologies if you are being asked this for the millionth time.
Thank you all.