Is it possible to avoid to select same dependent for a benefit?

Summary:

This is the case, the client has a benefit of "school help" for the soons of the employee. The employee can request the school help for each soon, so I added 5 options, Option SOON 1, SOON 2, SOON 3, etc. each one with a rate (more or less $2000 MX PESOS for each soon; if he request for 2 soons recieve $4000; 3 soons $6000).

The issue is :the employee could have only one soon/daaughter but he can request the "School help" for the same soon in the 5 options, is it possible to avoid choice the same soon in each option?

If the employee enter to each option he can choose the same soon/daughter in each one, is it possible to avoid it?