I think it's always smart to consider what you can do better--in any area of life, but especially with homeschooling.
But ultimately, if what you do works for your son and works for you, then you go with that. It doesn't really matter what your SIL (or anyone else!) thinks. If you and your son accomplish enough that you feel he's getting a good education, then it's okay.
Especially under the circumstances, with all that you have on your plate, I think you do just fine.
(But, of course, my opinion doesn't really matter either!
)
