Brother with line in BBC sitcom (2,6)

'bbc sitcom' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'brother with line' is the wordplay.
I cannot really see how this works, but
'brother' could be 'my' (both are expressions of shock) and 'my' is found within the answer.
'line' could be 'family' (family is a kind of line) and 'family' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?