Comments posted to our Dark Souls 3 Wiki
"(he has a lot of down-time during the fight; he's not constantly casting)" & "They are more than happy to teleport (which they always do behind the player, when the player not up against the walls in the room)"

Just absolutely and utterly wrong both times. Lothric spams those magic tricks as if his life depended on them, and Lorien teleports where he wishes, including in FRONT of the player.
His life do depend on them
He only casts if you aren't up lorians butt.
I'm trying to solo these motha****ers and I keep getting beaten in the 3rd phase! I only have so much stamina!
Dude .. its only second phase not 3 .. in second phase lorian attack still same but it combined with his brother
And lothric only revive lorian. Casting CSS like . And Light orb attack .
They are quite easy to solo up until the third phase... I thought this boss was easy until Lothric revived Lorian and had to fight them both AGAIN. I probably just don't conserve my estus enough. If it weren't for a 3rd phase they would be a piece of cake
also Lorian has way too much health for someone with sticks for limbs who can't even hold a sword... I beat them btw/ JS
Refined Warden Twinblades + Carthus Rogue produces dependable bleed outs every few hits with the two-handed double strikes. This can inflict 3 - 4k damage over the course of the initiating strikes and the bleed out proc itself. Unloading that onto Lorian when he is on his brother's back, then doing it again when he is on the floor healing, will make this a very short fight even up to NG+ levels. It's my fallback tactic. Summon a phantom if you have to in order to open up more chances to inflict bleeding.
Finally solod these to on NG+3. Bandit knife +9 with carthus rouge , and a lot of dodging. Don't even have any luck invested on the build.

Just Dont summon NPC.. its Useless
Lorian is weak if you can hit the right side of his hip. It will always cause him to stagger, leaving him open for crit. damage.
I summoned Orbeck for this fight and I managed to poise-break Lorian while Orbeck was directly in front of him, and he managed to perform a riposte on Lorian. I don't think it will be easy to recreate though.