Interesting question.
I'm very familiar with several siblings going to the same college to play baseball. A couple overlapped, and a couple didn't. I knew some twins that went to the same D2 (both on academic and athletic scholarships). They did extremely well there. Great opportunity for them.
My observation (among the older/younger siblings that I know) is the younger sibling gets the benefit of the doubt in the recruiting process. There is no question in my mind. One family in particular I know very well, and I know the younger son had D1 mid-major offers but no D1 P5 offers except where his older brother went and excelled. The younger brother's P5 career was less than ordinary. He would not have taken the D1 P5 offer if it wasn't for their academic "branding". In terms of baseball, he would have been better off (playing time) at the D1 Mid-Major. Obviously there are pros and cons, and each decision is unique to the opportunity.
Just my experience and observations.