For Crash 1, which I recently completed in the remaster, the first third or so of the game is pretty easy to let you get to grips with the controls, the final level of the first island is much harder but don't worry, Naughty Dog just sucked at difficulty curves back in Crash 1 and the game gets significantly easier ...
Both for regular and relics walkthrough easiest is Crash 2. For regular - Crash 1 is hardest. For Relics -... i think 3d and 1st are same. On Stormy Ascent level you can jump down in 1 or even 2 places - little short cuts for moving ladders.
Games like Overwatch, Fortnite, Call of Duty, and so on require online servers to play generally, although in the case of Call of Duty, you may be able to play its offline singleplayer campaign mode even without online services active.