try buying the revival earrings for the entire party, they're fairly cheap and will handle megaflare iirc
otherwise you'll need manawall + all, which should be useful for you through the entire fight regardless

aerith is actually really good for this fight tho i know you don't have her. her firaga (esp if you x2 it) really makes the gauge go up.

if you want to try this without grinding (it's probably doable? legit don't remember what the consensus at around your stats) you can get a lot of mileage out of cloud's counters and tifa's pressure stuff
starshower while he's counting down increases the stagger gauge iirc
constantly switch characters so that the AI is a bit slower
you should have 2 revival enabled party members for safety reasons as well

there's multiple ways of doing this fight on youtube and i honestly don't remember what i used but i did have to grind... unfortunately megaflare is awful; this battle takes quite a few tries to get through, and a lot of the vr stuff on hard assumes you'll be doing some materia grinding. i got through hard mode story without grinding but had to grind materia for the vr challenges, especially the stuff that comes after bahamut alone...
grinding is pretty easy once you have chapter 17 unlocked though, at the VR Center there. i think i spent like an hour and maxed most things out. if you're on hard mode, technically you can jump into any chapter at any time and come back, but i get if you don't want to do this.

goodluck!! it's a tough one!