Let W be the west shore, which they will all start from. Let E be the east shore, which is where they want to go.

1. A and C cross
W = { A, A, C, C }
E = { A, C }

2. A returns
W = { A, A, A, C, C }
E = { C }

3. C and C cross
W = { A, A, A }
E = { C, C, C }

4. C returns
W = { A, A, A, C }
E = { C, C }

5. A and A cross
W = { A, C }
E = { A, A, C, C }

6. A and C return
W = { A, A, C, C }
E = { A, C }

7. A and A cross
W = { C, C }
E = { A, A, A, C }

8. C returns
W = { C, C, C }
E = { A, A, A }

9. C and C cross
W = { C }
E = { A, A, A, C, C }

10. C returns
W = { C, C }
E = { A, A, A, C }

11. C and C cross
W = no one
E = { A, A, A, C, C, C }