Ok, here's the pattern link. Now you're starting with row 4, w&t and then work back on row 5 (mostly knits as you say). Now go onto row 6 for 10sts, w&t and work back on row 7. And yes, even when you work 26, 36, 39sts on the purl rows, you would be using the last 26, 36 or 39sts on the knit side, which would include the increases and decreases in pattern. Be sure to look at the pattern and make sure it's following the previous rows and not shifting or breaking the pattern you've established.
This will all be easier on the left side because you'll be working the pattern over, w&t and then just purl back.