First of all, I'd like to clarify that none of these are missable, as I've done them all in postgame after beating the final boss.
You can use a Bonfire Ascetic to respawn any bosses you missed and it'll still work with no problems.
Second, these are from my experience, there could slightly different/lesser requirements, but these are the things I myself had to to unlock these trophies.
Moonlight Greatsword (Inherit Benhart of Jugo's equipment)
You need to summon Benhart for 3 bosses and have him survive all 3 fights. You first find Benhart waiting by the entrance to Shaded Woods, after unpetrifying Rosabeth, talking to him will cause him to leave for the Bonfire after the dual Dragon Rider fight at Castle Drangleic. After that he'll be at the spot right after the main fight with the Pursuer, near the crow's nest, afterwards he'll be inside the Memory of Orro, where he will stay until you're done with his questline.
Here are the spots you can summon him at. (You only need to do 3 of these, I'm not sure if repeats count)
-The camp bonfire at Brightstone Cove. (Before the Prowling Magus fight.) (You have to have talked to him after unpetrifying Rosabeth for him to be available here.)
-Right outside the Looking Glass Knight battle. (Have to talk to him at Drangleic for him to be available here.)
-Memory of Jeigh down the stairs from where you start. (Have to talk to him at Crow's nest for this one.)
-Right outside the Throne of Want for Throne Defender/Watcher/Final Boss. (I've heard the final boss doesn't count, I can't confirm this myself.)
After summoning him for three fights and having him survive, talking to him inside Memory of Orro will cause him to give you his equipment.
Holder of the Fort (Inherit Captain Drummond's equipment)
Captain Drummond can be found inside the Memory of Vammar, to cause him to give you his equipment you need to defeat the Giant Lord in Memory of Jeigh. You can kill the Giant before meeting Drummond and it will still cause him to give you his equipment.
Lucatiel (Inherit Lucatiel of Mirrah's equipment)
Same deal as Benhart, here are the locations you can find her:
-Lost Bastille straight ahead from the Towers apart bonfire.
-No man's Wharf right by the bonfire.
-Earthen Keep at the bonfire right after the Covetous Demon.
-Black Gulch, near the first bonfire, if you light a torch and hug the edge, you should see a ledge, drop down there and she'll be waiting.
-Aldia's Keep, right by the 1st bonfire.
Here are the bosses you can summon her against:
-Versatile Sentry at No Man's Wharf. You'll find her summon sign at the switch that opens the shortcut through the 2nd level of the Wharf. (Have to talk to her at Wharf for it to appear)
-Lost Sinner at Sinner's Rise. You'll find her sign right at the elevator that drops you to the Sinner fight. (Have to talk to her in Bastille for it to appear)
-Smelter Demon at Iron Keep. Sign is right outside the boss fight. (Have to talk to her at Earthen Keep)
-The Rotten, sign is right next to the hidden bonfire at Black Gulch. (Have to talk to her in Black Gulch)
After the 3 fights, talking to her at Aldia's Keep will cause her to give you her equipment.
Smith For Life (Inherit Steady Hand McDuff's equipment)
After giving McDuff the Dull Ember found in Iron Keep, light the torch in his room to have him move away from the chest he's sitting on, after that, spend a total of 50 thousand souls on his wares while also having 10 thousand of those souls go into weapon infusion.
Garrulous Miser (Inherit Laddersmith Gilligan's equipment)
After Gilligan moves to Majula, spend 12 thousand souls to build his biggest ladder and he'll reward you with his equipment.
Reflections on Disembodiment (Inherit Head of Vengarl's equipment)
After finding the Head of Vengarl in the Shaded Woods, keep talking to him until he mentions his body, after that, learn his gesture. Next, you'll find his headless body after defeating The Duke's Dear Freja, after defeating his body, return to him and exhaust his talk options and he'll reward you with his equipment.