I'm still working on my earliest HOF imageevent link that will hopefully supplant the oldcardboard website (which hasn't been updated in years). Unfortunately, I'm only up to Brouthers, but I have everything checklisted that I need. Here's a sample from Aaron to Brouthers:
https://imageevent.com/derekgranger/hofearliest
Anyway, ignoring the few 19th century composite cabinets like the 1894 Betz Studio with 7 HOFers, which included "rookie" images of Jennings, Keeler, Kelley, and McGraw; the 1886 Lorillard's Team Cabinets w/ Sam Thompson, etc.; as well as the various early- to mid- 1900s W601 Sporting Life Team Premiums and 1906-07 W601 Team Postcards w/ early images of Cobb, Huggins, Branch Rickey, etc., there simply aren't that many that fit the mold of 2- or 4-player images. I assume also that you aren't interested in multi-player cards like team postcards/cabinets, which could significantly add to the total.
Based on my list, you
could conceivably include the following pre-war cards as "rookie" issues:
1931-32 "4-on-1" Exhibits w/ Luke Appling
1941 Double Play w/ Lou Boudreau (although his '39-46 Exhibit is often credited as his "rookie" issue)
1931-32 "4-on-1" Exhibits w/ Joe Cronin
1931-32 "4-on-1" Exhibits w/ Bill Dickey
1936 R314 Goudey Wide Pen Premiums w/ DiMaggio & McCarthy
1929-30 "4-on-1" Exhibits w/ Leo Durocher (and some other guys named Ruth and Gehrig)
1937 "4-on-1" Exhibits w/ Bob Feller
1931-32 "4-on-1" Exhibits w/ Rick Ferrell (name spelled wrong and not his image...haha!)
1936 All-Star Game Ticket Stub w/ Ford Frick (R), Will Harridge (R), and Kenesaw Landis
1909 Boston Herald Supplement w/ Harry Hooper
1929-30 "4-on-1" Exhibits w/ Heinie Manush
1938 "4-on-1" Exhibits w/ Johnny Mize (although 1936 R312 National Chicle is widely regarded as his "rookie")
1929-30 "4-on-1" Exhibits w/ Mel Ott (ignoring his R316 Kashin and 1929 Leader Novelty)
1941 Double Play w/ Pee Wee Reese (although his 1940 Brooklyn Team Issue and 1941 Play Ball are widely regarded as his "rookie" issues)
1941 Double Play w/ Phil Rizzuto
1941 Double Play w/ Enos Slaughter (ignoring his 1941 W754)
1909 Boston Herald Supplement w/ Tris Speaker
While there are some cards and images that slightly pre-date or are concurrent with the Exhibits, I think you could make the argument that each of these are "rookie" issues. I may have missed one or two...hope this helps!
edited to add:
I don't think any of these Exhibits include "rookies" for two HOFers simultaneously other than the Slaughter and Mize (that's a stretch), as mentioned previously. If you want to stretch things even further, the 1936 All-Star Game ticket stub with images of Frick and Harridge could fit the bill.