"Armhole shaping: Next row(RS), BO 5 sts, knit 1 more st, work in patt as set to last 7 sts, knit to end. Next row(WS), BO 5 sts, p6, k1, PM, work in patt as set to last 8 sts, PM, k1 purl to end, 94 sts.
*Dec 1 st at each edge every RS row 3 times as foll: ssk, knit to 1st before marker, p1, work in patt as set to marker, p1, knit to last 2 sts, k2tog* 88 sts. Next row(WS), purl to marker, remove marker, p1, k1, PM work in patt as set to last 7 sts, PM, k1, purl to end removing original marker. Beg with next row (RS), rep btwn *, 82 sts rem after armhole shaping is complete."
I've bolded the markers. In each case I see 2 of them.
Work to the last 7 makes is incorrect, you're right. It should be work to the last 9sts PM, work to the end, removing the old marker.
And yes, repeat the RS decrease row until there are 82sts.
I think this is going to be easier to do if you follow the instructions (with that one correction) with the sts on the needle than it is to read the instructions. It's really trying to guide you through the decrases while maintaining the pattern st as much as possible.