You don't need separate material for everything. I used CAT material and added past XAT DM papers + NMAT mocks. Time management becomes the real game as exam dates get close. Don't worry, just remember that practice is key and you'll do great. 

SNAP and NMAT are more speed-based, so even if you're good at concepts, you'll struggle if you don't train for time pressure. I used 15 minutes sectional drills to adapt after CAT. If you're starting prep late, pick CAT + one backup like NMAT or SNAP. XAT requires decision-making practice, which is very different. I started DM prep after CAT and it was enough. 

Don't try to juggle all four from day one. Build strong concepts for CAT first-it'll automatically help in SNAP and NMAT. Start tailoring your prep for each exam two months before their dates.

I focused entirely on CAT till November and then used December to tweak my prep for SNAP and XAT. Honestly, the basics of QA and VARC overlap a lot. Only DM in XAT and adaptive format in NMAT need separate attention.