Fill a cell with random values by drawing from certain cells in Google Sheets

[Marco215]

Hello everyone and thanks in advance to anyone who can help me,
I'm creating some scoreboards for tournaments.
After the initial phase, the fished-out players (below in red) access the elimination phase (SEMIFINALS) by placing themselves randomly in the scoreboard (below in the "?" cells in red), so I need to fill one or more cells randomly by "fishing" from previous cells.
If a player goes to match #9, the other will have to go to #10. A player cannot go to both matches.
How can I do it?

https://docs.google.com/spreadsheets/d/1X46auATNaOwp0ID0P5bRG1A3c61L0LJS1S3Y6dNluZQ/edit?usp=drive_link

 

[Marco215]

Any suggestions?