Relative of rising favourites runs into trouble (11)

'relative' is the definition.
(stepbrother is a kind of relative)

'rising favourites runs into trouble' is the wordplay.
'rising' says the letters should be written backwards (going up in a down clue).
'favourites' becomes 'pets' ('pet' can be a synonym of 'favourite').
'runs' becomes 'r' (cricket abbreviation).
'into' is an insertion indicator.
'trouble' becomes 'bother' ('bother' can be a synonym of 'trouble'**).
'pets' back-to-front is 'step'.
'r' placed within 'bother' is 'brother'.
'step'+'brother'='STEPBROTHER'

'of' acts as a link.