Your opponents can choose not to pay to attack with a creature that attacks “if able.” If there's no other player or planeswalker to attack, that creature simply doesn't attack.
2019-10-04
In a Two-Headed Giant game, creatures can attack your teammate and planeswalkers your teammate controls without requiring a mana payment.
Flying
Protection from white (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything white.)
Creatures can't attack you or planeswalkers you control unless their controller pays for each of those creatures.
for each of those creatures.