Alex, Bert, Carl, and Dave are all brothers, with two of them being twins. At least one of them is a knight and makes all true statements. At least one of them is a liar and makes all false statements. And at least one of them is a knave and makes alternating true and false statements. The two which are the same type are the twins. From the statements below, determine who the twins are.

Alex:
1) Bert is one of the twins.
2) Carl is a liar.

Bert:
1) Carl is one of the twins.
2) Alex is a knight.

Carl:
1) I am not one of the twins.