Guage and sizes

I taught myself to knit in 2007 while I was spending many hours in a hospital caring for a family member. Recently, I’ve started knitting again and have found a pattern that is similar to bed slippers like my husband’s grandmother used to make for us.
Grandma made these in multiple sizes but I cannot find a similar pattern that provides info on making them for smaller adults or children? Is there a standard method for decreasing the size?
Also, I am confused about the instructions on Row 28. Previously in the pattern, you knit 9 before adding a purl, but this says to only knit 7. But then for row 30, you go back to knitting 9 and then purl 1. Why would row 28 only knit 7?

I’ve tried using kneedles ranging in size from 6 to 10.5 and have not seen a huge difference in the size of the slipper. Grandma always used double yarn, so I’ve been doing that just using the super saver yarn from the fabric department at the discount store. However, I began the 3 decreases at row 40 and immediately jump to row 49 (k2,p2) and finish with row 59. Otherwise the slippers are way too long.
Any suggestions would be greatly appreciated.

Row 28: With single strand, k 7, p 1, pick up second strand, k 1, inc 1 st, k 9, inc 1 st, k 1, drop extra strand of yarn, p 1, k to end of row-31 sts.

For row 28 you’re going to k7, do a p1, k1 and then increase in a st (knit front and back for example). This pattern takes the place of the k9,p1 but also uses 10sts. And here you’ll pick up an extra strand of yarn to make the sole of the slipper thicker. You can do this or not as you wish.
Here is a similar pattern with directions for 3 sizes.

I took a few days off from knitting the adult slippers to try some baby booties. So, I’m back to this today. I’m still confused about row 28. By using k9, p1, k9, p1, k9 pattern on even rows from 2 to 26, the pattern creates a ridge/line that becomes the edges of the sole once the heel is sewn together. If I only k7,p1 for row 28, it moves the ridge/line over by two stitches for row 28. Then for Row 30, it says return to the pattern used for Rows 1 and 2 which is k9,p1,k11 (modified for extra stitches),p1, k9. At least this is what I’ve assumed I should do for even rows beginning with 30 as it only says continue as for rows 1 and 2.
Does this make sense about the ridge/line moving two stitches?

I read the pattern the same way you do. It very deliberately moves the ridge over 2 sts and I’m not sure why. You can try it and see if the reason becomes clear when you work the row or you can continue with the ridge st as you have been doing, 9sts in. These slippers were one of the first patterns I made when I learned to knit but the pattern changed to stockinette for the toe.

Thanks Salmonmac. I did try following the pattern this morning to see if it would generate something different than what I thought. After having read some of the forum posts, I inserted a lifeline (I think that is the right term) at Row 27, then knit Row 28 as instructed. It did move the ridge/line. I knit on to Row 40 but then being as I am, I was not happy with the way Row 28 looked and raveled back to Row 27.
I’ve seen this same pattern online for a number of years and was just curious that it seems to have never had a correction made.

OK, good to know. Maybe there’s someone at the website that you can email to make the correction? (or maybe they can think of a reason for the shift.) Post a picture if you like so we can see the finished slippers.