Spinosaurus, and Ceratosaurus are accurate size to their movie (JP3) portrayals.
As in JP3 - Spinosaurus was actually slightly smaller than the real life version. In real life version - Spinosaurus has been estimated at about 13.4-15.24 meters/44-50 feet, The JP 3 Spinosaurus - is about 13.4 meters/44 feet, about 6 meters/19.7 feet tall at the top of the spines. In the movie Spinosaurus looks so large because it faced off against a small sub-adult T,rex.
Still - if Frontier based the game T.rex - off Rexy's (the T.rex from JP, JW, & JW:FK) JW stats - then it could definitely make the Spinosaurus seem to be smaller. In JW & JW:FK - Rexy is a fully grown, old T.rex (at least 27-30 years old) - being 13.4 meters/44 feet long, 5.1 meters/16.8 feet tall.
By comparison - the JP3 Ceratosaurus is actually about 2 meters longer than it's real life counterpart - about 9.14 meters/30 feet in JP3 vs. 7 meters/23 feet in real life .
Diplodocus was never actually in a JP/JW movie, to date. But if they based on real life like they have with Apatosaurus - then it should be about 25- 33 meters/82-108 feet long