Binding off for leg openings

This is my second dog sweater so I know I’ve done this before, but I can’t for the life of me remember what I did! I’m on the row that begins the leg openings so I have to bind off some stitches.

I am supposed to do seed stitch for 10 sts then join a second ball of yarn and with that ball bind off the next 8 sts. What I’m unsure of is do I use the previous stitch before the bind off (the 10th stitch) in the bind off as the stitch I slip over? Or will I be slipping over the second stitch in this set of 8 stitches?

So…
Seed Stitch 1-10 K1, slip 10th stitch over

OR

Seed Stitch 1-10 K1, P1 slip knit stitch over

The second choice.
Seed st the 10sts, then start the bind off with 2more sts (stitches 11 and 12). Slip stitch 11 over stitch 12.

Thank you so much! You’ve been very helpful with all of my beginner questions, I swear I’ll figure out what I’m doing eventually.