For Nightmare, besides HP (especially for the poor squishy Ranger), my second goal would be a bit more to-hit for both if possible.
for Fighter: Sash of Sinew, Bead of the Bull, Stalker’s Bracelets, Lenses of Heimdall Sight or Goggles of Anticipation if you have extras (these seem to not be as cheap as maybe I think they ought to be), plus Venomguard Greaves to mostly mitigate the penalty from your Gauntlets of the Midgard Serpent. I would also consider replacing Greater Holly Ring with Fortitude or Iron Will.
for Ranger: not a couple of dollars, but do you have a way to get this build to level 5? That'll help significantly with HP. Then, in addition to all BeLinda's excellent suggestions, ditch melee-focused wrist and Charm of Fire Newt and IS Stalker's Prism, give the +2 Savage Sword to the Fighter, grab Bracelets of Frail Agility, Goggles of Striking, and pretty much fill in any remaining slots you can with +HP tokens (start with
this search
and then filter by slot) including e.g. uncommon IS Tsavorite Prism.
FWIW, the way things stand right now, if you only have 1 Shoes of Nethercraft I'd give it to the Ranger instead of the Fighter -- not that Boots of Agility aren't also good for this build if you can find enough HP elsewhere, but 27hp is just not nearly enough for Nightmare.