Yokels' relatives in birthday ritual (8)

I believe the answer is:

bumpkins

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'yokels'' is the definition.
('bumpkin' can be a synonym of 'yokel')

'relatives in birthday ritual' is the wordplay.
'relatives' becomes 'kin' (I've seen this before).
'in' is an insertion indicator.
'birthday ritual' becomes 'bumps' (I can't justify this - if you can you should believe this answer much more).
'kin' put within 'bumps' is 'BUMPKINS'.

Can you help me to learn more?

(Another definition for bumpkins that I've seen is " from the country".)

I've seen this clue in The Sun.

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