"All sizes: Continue pattern. At the same time when the piece measures 8-7-5-4-3-2 cm inc. for sleeves each side on every other row: 2 sts 2 times and 26-26-26-46-46-46 sts 1 time = 151-155-163-203-209-215 sts. Incorporate new sts into the pattern ..."
Is this the part that's causing the problem? You can do the increases with the same working yarn strand. It may be easiest to cast on these sts at the beginning of a row. So if the RS is facing you, ready to be knit, cast on 2sts then work across to the end of the row. Turn as you usually would, cast on 2sts and work to the end of this WS row. Repeat. On the next row, cast on 26sts at the beginning of the row using a knit or cable cast on, work across these sts and then across the rest of the row, turn and again cast on 26sts and work across the new sts and the rest of the row.
It's a very interesting pattern that looks great. Should be fun.