The old relative follows a river to high point (10)
I believe the answer is:
apotheosis
'high point' is the definition.
'apotheosis' can be an answer for 'point' (I have seen 'Crowning point ' mean 'apotheosis' so perhaps 'point' could also mean 'apotheosis'). I'm unsure of the 'high' bit.
'the old relative follows a river' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'relative' becomes 'sis' (short for sister).
'follows' means one lot of letters go next to another.
'river' becomes 'Po' (Italian river).
'the'+'o'+'sis'='theosis'
'a'+'po'='apo'
'theosis' put after 'apo' is 'APOTHEOSIS'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for apotheosis that I've seen before include "glorification" , "sublimation" , "crowning moment" , "Ultimate transformation" , "Highest point of development" .)