Which sentence is incorrect because it's not parallel?
For my next birthday, I decided either to play volleyball and picnic at the beach or to take the group out for dinner and a concert.
For my next birthday, I decided on either playing volleyball and picnicking at the beach or taking the group out for dinner and a concert.
For my next birthday, I decided on either volleyball and a picnic at the beach or dinner and a concert for the group.
For my next birthday, I decided we're either playing volleyball and picnicking at the beach or to take the group out for dinner and a concert. @mikkel9

Question

Which sentence is incorrect because it's not parallel?
For my next birthday, I decided either to play volleyball and picnic at the beach or to take the group out for dinner and a concert.
For my next birthday, I decided on either playing volleyball and picnicking at the beach or taking the group out for dinner and a concert.
For my next birthday, I decided on either volleyball and a picnic at the beach or dinner and a concert for the group.
For my next birthday, I decided we're either playing volleyball and picnicking at the beach or to take the group out for dinner and a concert. @mikkel9