Sorry, if it was misunderstood by me.
Maybe the following is more helpful for you to develop a solution?
https://forum.getodk.org/t/randomly-select-a-name-from-age-group-under-5-5-15-over-15/20696
(Don’t worry, please, about the “random” aspect here.) The join creates here a person “list” in a string, separated by blanks. The string/list elements can than be adressed/separated with selected-at(…) and count-selected(…) function.
Perhaps also the new select from repeat option might be interesting for you
https://docs.getodk.org/form-logic/#generating-select-ones-from-repeats
But also be aware of (@Kal_Lam for status news?) https://community.kobotoolbox.org/t/having-issues-with-select-one-from-repeats/20039.
Might be further adapted with appearance and read_only.
