I think the Suffolk CC to Stony Brook path is really good option, especially for STEM. Not sure if both your sisters are interested in STEM. Also this is not an either or thing, you can always encourage your sisters to apply to a few four year colleges and see how the admissions and financial aid go. And encourage them to a four-year if you think that’s the best course for them.
I lived in Poughkeepsie, the local c/c was Dutchess, and many people went there and then SUNY or Marist (local LAC) or private. It’s a good system, as you probably know.