First of all, I applaud you for taking the time and making the financial commitment to a trip back east to look at schools. Sounds like your son had done a good bit of legwork to already narrow down what type of school he wants to attend and what his baseball options are. Also impressed you guys have already figured out the merit scholarship potentials out there.
Now, about the connecting with the coaches at these schools:
First of all remember this is a very busy time of year for them. Even for the RC who is an acquaintance of your son's freshman coach, don't take it personally, but just know these coaches right now are doing 12-14 hour days with fall ball. Doesn't mean one of them won't reply tomorrow, but "cold emails" need to have something "hot" about them to draw attention of these coaches. Especially since you are reaching out to them.
Did your son attach a spectacular highlight video link to the emails he sent? Did he put an attention getting phrase in the "email topic" box? Was there something in the email worthy of them clicking?
During my son's recruitment, there were plenty of schools where we "stormed the gates." Basically did what you're doing, had sent emails and received no replies but we did the campus tour and then ambled on our own over to the ballpark. Sometimes you can meet a groundskeeper, sometimes an AC, and sometimes you catch the HC leaving his office going to a funeral (as son and I did once, and this Legend of a HC gave son a good 15-mins of his time, I'll never forget it).
So keep emailing these coaches, up to the point where you're on the campus for the admissions tour. Be sure to add a quality video or a great topic heading to catch their eye. Has the freshman coach who knows one of these guys made a phone call for your son? That should not be difficult for him. Regarding email topic heading, I'd throw in his GPA and hopefully one other strong stat, like his 60-time, or velo, or ACT score, or whatever. He has to have something to make them "answer the door." If he can introduce himself via email and make a good enough impression it is a no brainer for any coach to find 30-mins of his day to meet with you. It's no sweat off their brow, as long as it's worth their time and could save them a night in a hotel room. Obviously they need to see him play, but by a quality introduction on one of these campus visits it could certainly make them curious to make sure to see him play next summer.
One last thought, you still have time to expand your trip itinerary and widen your search and continue to send emails WITH VIDEO to coaches at other schools. You never know who will reply to you? Someone will. Widen your search and when you get some replies, then consider dropping the non-reply schools from your itinerary. I'd also hit up 2-3 D3s while you're here if you can.
Good luck and keep us posted as to how the trip goes.