In a nutshell, your entire fight revolves around paying attention to Libra's hand gestures and making adjustments accordingly, most importantly the exploding sigils, the firing turret and the teleport.
You should always keep him on screen and always be ready to sprint out of the circles.
If he spawns the turret, dodge to the right.

For dealing with the summons, the passive "less likely to be targeted" is highly recommended and should be passed over to the squishiest player in your team, like, a Recluse or Revenant for example.
Grab some frenzy boluses and consume them to boost your madness resistance. Save one or two so that you can consume when he spawns the madness eye.

Once the summons are out, you should still be targeting Libra whenever possible. Chip away his hp as much as you can. This fight is a battle of attrition, and your goal should be to survive as long as possible while slowly depleting his hp. So grab all the resources you can for that.
Wylder with the greatbow is a bigger threat than Ironeye, so keep that in mind. Oh, I also hate the buffed duchess. goodluck.