As I understand it if no candidates receives a majority the house of representatives would chose a president among the top three candidates, but what happens in (the unlikely) scenario where there's a tie for third candidate.
The simplest example is with four candidates: if Washington gets 268 votes, Adams 134 votes, Jefferson 68 votes and Madison 68 votes
Also there is a (even more unlikely) scenario when the very top is involved in the tie. If there's a complete tie among more than three top candidates. For example: Washington, Adams, Jefferson and Madison each got 134 votes (and Monroe got 2).
How would it be decided which of the candidates would be eligible for selection by the House of Representatives?
To be clear this question is not the same as "What happens if no candidate reaches 270 electoral votes?" since that only addresses the situation where no candidate gets 270 votes and touches the situation when two candidates gets 269 votes each.