You can allocate 25% to yourself for all 3 boxes or depending on who the other person was or the person who paid the premiums, you can allocate 0% and they can claim 100%. You must all agree on the allocation amount if you are going to split it up in any way other than by the number of people on the policy.
If the other people were your parents, it is a good idea to make sure they did not claim 100% prior to you entering a number. All numbers must add up to 100%.