:?? I'm clueless as to why they want you to mark that row for the sleeve cap. It appears to be straight across the top, so seaming should be pretty simple (even simpler if you get your mother to do it :teehee: )
You bind off under the armholes on the body, so that 1 1/2 inches that you marked match up to the armhole bind-offs. I think it would be obvious without marking them, but maybe it's a case of too much information.