Assign a short coding challenge and rank candidates on their solutions.
Then, one at a time, hire each candidate as a contractor for 20 hours of work. Let them fix bugs and do code reviews. See how effectively they communicate through code and in code reviews. Invite them participate in the weekly standup meeting.
Finally, have team members who worked with the person write confidential feedback with a hire/no-hire rating and justification. Hire the first candidate who gets all 'hire' ratings.