Possible Clues:

• Papa's papa, perhaps (In this clue's answer, note letters 5-6 and 8-9)
• An alternative relative in US expressions like “the mother of all traffic jams”
• Oldster's greeting managed to shoo ducks away before two daughters come in
• Pop's pop
• Pa's pa
• After piano, daughter put on variable pop for old man
• Older relative