Old men with power like propping up old royal (8)
I believe the answer is:
grandpas
'old men' is the definition.
(older relatives)
'with power like propping up old royal' is the wordplay.
'with' becomes 'and'.
'power' becomes 'p' (symbol in physics).
'like' becomes 'as'.
'propping up' means one lot of letters go next to another (in a down clue, some letters hold others up).
'old royal' becomes 'GR' (Georgius Rex, name for King George).
'and'+'p'+'as'='andpas'
'andpas' put after 'gr' is 'GRANDPAS'.
(Another definition for grandpas that I've seen is " Relatives".)