You do not need to use double point needle to do Tw2f. It can be done on straight needle.
Here is how to do it;
Insert right needle into the back loop of the second sts on the left needle and knit into it but don't slip it off the needle. Knit the first stitch as usual then slip both sts off at the same time.
Here is a video on Tw2f which is exactly the same way as C2B