Of your choices the Nikon 7500 looks best. Here's a low light comparison of your 4 cameras raw at 6400 ISO:
https://www.dpreview.com/reviews/image- ... =1&x=0&y=0
Consider also the Canon 6D, a great
FF camera that you can find on EBay for $550 or so (body only). I added a link also with my own Fuji X-a1 that is very hard to beat for $150 on EBay (body only).
https://www.dpreview.com/reviews/image- ... =1&x=0&y=0
You may want to consider an articulating screen because bending your neck for alignment gets old real quick. Like JT said, consider the weight as well. Th Fuji X-a1 is a super light system camera with articulating screen, I am sure the other DSLRs are heavier.
Then of course you can have one modified for IR filter removal by LifePixel, or buy a modified camera from them. It will boost the IR photons and will reduce noise after color normalization.
... Henk.
Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80,
Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall,
Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS,
DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles,
Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50,
Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK,
Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17",
Website:Henk's astro images