You choose the player, planeswalker, or battle each Warrior token is attacking. They don’t all have to attack the same one, and they don’t have to attack the same player, planeswalker, or battle as the creature with mobilize.

Although the Warrior tokens enter as attacking creatures, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won’t trigger when the tokens enter attacking.

The number of creatures you control is counted at the time the activated ability resolves. This means that an opponent can respond by destroying your creatures to reduce the amount of damage dealt.