Seriously, two homes require internal attention (2,7)
I believe the answer is:
in earnest
'seriously' is the definition.
(synonyms)
'two homes require internal attention' is the wordplay.
I cannot quite see how this works, but
'attention' could be 'earnest' (I have seen 'serious attention' mean 'earnest' so perhaps 'attention' could also mean 'earnest') and 'earnest' is found within the answer.
The remaining letters 'in' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for in earnest that I've seen before include "showing determination" , "with serious intent" , "With serious intention, not fooling about (2.7)" , "Sincere and serious" , "Not joking" .)