It's unusual to include the taxes (6)
I believe the answer is:
tithes
'taxes' is the definition.
The answer and definition can be both related to property as well as being plural nouns.
Perhaps they are linked in a way I don't understand?
'it's unusual to include the' is the wordplay.
'unusual' indicates anagramming the letters.
'to include' is an insertion indicator.
'its' with letters rearranged gives 'tis'.
'tis' going around 'the' is 'TITHES'.
Can you help me to learn more?
(Other definitions for tithes that I've seen before include "Tenth parts, levied by some churches" , "Tenths of income once paid to church" , "Church taxes" , "Tenth portions of income given to church" , "Tenths of income given to church" .)