Some practical advice I would offer would be as follows:
(a.) drive right into the parking garage that is right next to the Steamtown acerage. You will be able to walk from the 2nd Floor of the attached mall to go right out onto a pedestrian bridge that reaches directly into the train yard. Plenty of food places are in the mall for snacking.
(b.) you can enter the whole Steamtown yard via the pedestrian bridge which ends in the RRyard with a gradual sloped walkway that will take you down to the ground right near the Big Boy that is featured outside there. The bridge affords you broad perspective on the whole exhibit and provides a view directly down onto passing trains under it, on occasion. (However, don't make the mistake of standing there, looking downward, when a steam engine passes beneath you - what a hot face-full I got !!!)
Using the pedestrian bridge is how I accessed and explored the place, which required less walking than entering from street-level, a few years ago. My suggested plan for approaching the exhibit tries to give your companions a bit of a break on the distances to be walked.
Some changes to Scranton since Frank M (Monsoon's) last visit: The new Marketplace at Steamtown now charges for parking. Enter Steamtown via Lackawanna Ave. 350 Cliff St is the GPS address you will need to get to the parking lot. There is also a bus station near Steamtown's entrance, so it isn't as obvious as it once was. You can still access the pedestrian ramp from the Steamtown parking lot.
For train operations, don't expect any to take place on a Monday. For 2018, the Scranton Limited trains run Wednesday through Sunday. You might catch freight movements, which can be really cool, but not scheduled. The non-railfan typically likes Steamtown due to the fact that the exhibits deal with history, work, travel, construction, and explanation of machinery in simple language. There are plenty of trains to keep the rail enthusiasts happy. You might want to stop in at the Radisson Lackawanna Station Hotel, which is the former train station. It is beautiful inside. You can also get a bite to eat along with an adult beverage alongside the tracks. If you like Irish pub style restaurants, Scranton will be your type of town. There is also a vegan restaurant.
There are railroad yards for the Delaware-Lackawanna, Norfolk Southern, Reading & Northern and Luzerne & Susquehanna nearby, in addition to the Trolley Works where restoration of the trolleys takes place, and the Erie Lackawanna Dining Car Preservation Society. Trains are everywhere, but not all locations welcome tourists.
If you want more info, you can PM me. There are plenty of Scranton-based people here on OGR who can add to the things you might find interesting. There is no RailRiders baseball game on Monday, July 23, so that is out.