I am guessing that now they want you to work on the two legs at the same time so that you will have an exact match in each leg for decreases and length. In that case, you need two balls of yarn. If you have only one ball remaining, you could knit from either end of the skein to get the same effect, though it can be a little awkward.

I am not sure what you are doing to knit the legs. Usually you cast off at the beginning of a row. But here I am guessing that they are having you cast off one stitch at the end of the right leg and then that gap is the crotch, the separation for the two legs. You will also be donating the last stitch after the cast off gap to the left leg it seems to me as you pick up the stitches from the holder???

Where does it say to cast off from the original leg? I don't see it in your instructions you copied for us.

Does what I interpret make sense? Do you need to share more of the instruction wording?

Hmm, I think you're right - do the second leg on a new strand or ball. The first leg is on stitch holder, which is why I wondered if I was supposed to use the same strand somehow.

The instructions are pretty sparse, and I included everything for the second leg. Following that, it's just "Cont on resulting 53 sts." For the second leg, the instructions say to Cast On, not Cast Off at the end of the row, which I guess creates a bridge (crotch) between the two.

Thanks for this. I will try it. I'm so lazy I didn't want to do it and tear it out, but really, with 26 sts, I shouldn't worry about that!

I'm also grateful that you replied so fast. I keep only one project on the go at any time because I'm notorious for not completing projects, so I was completely stopped in my tracks. (Confessions of a lazy knitter...)

No, I suspect you do both legs together until you creat the crotch. At that point, you need to switch to two balls of yarn because the legas separate there. Until then, you are making one solid piece going over the hips.