Help with buttonholes!

I’m stuck on making these darn buttonholes!
The pattern initially read:
Next Row:Rib 4, cast off 1 st, (rib 15, cast off 1 st) 4 times, rib 3
Next Row: Rib 4, cast on 1 st, (rib 16, cast on 1 st) 4 times, rib 4

I found these buttonholes were way too small so a kind reader gave me this pattern to increase the cast off to 2 st.
Rib 3, cast off 2 st, (rib 14, cast of 2 st) 4 times, rib 3
I’m okay to this point but am stuck on the pattern to do the second row. Would it be:
Rib 3 cast on 2 st, (rib 15, cast on 2 st) 4 times, rib 4?
Also, when casting the stitches back on, I have them end up on the left needle, so do I then just knit them in pattern to get them on the right needle? Obviously I’m new to all this so I hope someone can help. Thanks

So I think that row 2 would be rib 4 cast on2(rib 15, cast on2)4 times and finally rib 3. But really this is easier to do by looking at the sts than it is to write out and follow. Just look at the sts and when you get to the cast off sts, cast on two. Look at the ribbing and knit the sts that look like knits and purl the purls and you’ll be fine.
When you come to the place where you need to cast on, pass the right hand needle to your left hand and cast on the 2sts (knitted cast on works well here). Once the 2sts are cast on, move the needle back to your right hand and continue with the ribbing. on the next row you’ll be able to rib acros all the sts.

Thank you once again Salmonmac; got it this time!! Hooray!