Two pianos a part of the family (7)

I believe the answer is:

grandpa

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'a part of the family' is the definition.
(I know that grandpa is a type of grandparent)

'two pianos' is the wordplay.
'two pianos' means two replacements for 'piano'.
'piano' becomes 'grand piano' (grand piano is a kind of piano).
'piano' becomes 'pa' (I can't explain this - if you can you should believe this answer much more).
'grand'+'pa'='GRANDPA'

Can you help me to learn more?

(Other definitions for grandpa that I've seen before include "Parent's father" , "much older relative?" , "Veteran" , "Old man" , "family member" .)

I've seen this clue in The Times.

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