When using an Alternate Team Ability (ATA) on characters must the ata be used on all of the CHARACTERS or can it be used on some of the characters? Not sure how ATA's are to properly be used.

Page 18 of the rule book:

ADDITIONAL TEAM ABILITIES
Additional Team Ability (ATA) cards can be added to your force if the characters on your team meet the prerequisite listed on the card. Each ATA card indicates the cost per character that must be added to your force in order to use it in the game; all characters that meet the prerequisites must be assigned the ATA and your force’s Build Total is affected accordingly. ATA cards provide either different or additional team abilities to the qualifying characters on your force. These team abilities are possessed by the qualifying characters and can be used by wild cards (unless the ATA specifies otherwise). A force may only include one ATA card.

So if every character on your force meets the prerequisite, then they all must be assigned the ATA. If only 1 meets the prerequisite, then only that 1 is assigned the ATA. And every permutation in between.

Thank you.