Yes, I think you're right, increase at both ends on the RS rows. There's a missing increase near the end of row 3 in the instructions. Usually these patterns are symmetrical and so the row should end with a knit to the last 2sts, m1, k2. Then the instruction to repeat increase on each edge of RS rows makes sense. Since you've already increased 4 sts however, you'll only need to repeat the increase 9 times in order to get to the 22st increase from the cast on (48sts + 22sts=70sts for the smaller size).
You'll slip the first st of the row in order to make a clean chain on the edges which will look neater than working both the first st and the last st of the row. The RS rows end in a knit st, so knit that last st.