Opposition leader Raila Odinga is set for a tough decision-making task ahead with regards to the looming Migori senatorial by-election.

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The seat fell vacant after the death of former Senator Ben Oluoch Okello who succumbed to cancer last month, with Odinga obviously keen to have it remain in his ODM party.

However, two sons of the late Senator have since emerged to battle for the position, worsening the situation for Raila who was most likely to rally behind his ally and former Rongo lawmaker Ochilo Ayacko.

Willis Oluoch Okello and Mark Okundi both submitted their papers to the ODM party on Friday, in a move likely to set the stage for sibling rivalry.

Okundi went ahead to declare his ambition despite the family confirming that it had agreed to back Oluoch for the slot, with a source telling the Daily Nation that he was discontented with the decision.

"We had agreed that Mr Willis Oluoch but Mr Okundi was not pleased as he was expecting to be endorsed. He chose to stick to his guns," the source is quoted.

This is likely to leave Odinga with a very tough decision on who to back and could see another party's candidate emerge the winner due to disunity.

Ayacko has since withdrawn his petition challenging area Governor Okoth Obado's August 8 reelection in preparation for the pending by-election.