Congrats to you, and your teammates on the survival of a HC run. I have always tried on Mayday Solo or plus 1 teammate. The difficulty doesn't get too overwhelming unless we add more teammates. That is where I begin to struggle...
Regular ammo +2, another guy running special ammo+2
body armour +4, maybe 2 people running it
feral instinct +4 for extra duration and somebody doing hand boosters
+3 on medic with its reviving teeth ability.
+2 sentry guns
if any remains, + 1 pistols and other stuff.
for score runs, just a few tips. explosive ammo will kill you quickly! bad ammo choice on this mode! portable turret and most other things will damage you when shooting at team mates so relic runners can use the grenade turret as it does not.
activate the traps and almost always be mobile.
I had a friend do 1 relic when his first PoC hardcore co-op escape and he was top 500 for it XD