Note: "Ones" means 1st corners, "Twos" means 2nd corners.
A1: Ones meet; twos meet. Ones cross R; turn single L; twos the same.
A2: All that again.
B1: Ones R-hand turn half-way; twos join in and star half-way. Ones set while twos turn half-way; ones turn single while twos set.
B2: Ones L-hand turn half-way while twos turn single; twos join in, star half-way. Progression: Ones fall back; move diagonally R, in front of neighbour who falls straight back. (Twos move diagonally L as ones start the next round.)
Last time: Ones turn single as twos progress.
Don't come in too far: the next round starts with ones meeting while twos move diagonally left to progress.