u/SkittlesMcflurry9999

Sadly this trophy is becoming one of the only things stopping me from getting the platinum and no matter how many rounds I do we've never been able to even spot it, I've managed to find some videos finding it online so I'll always check those spots but with no luck, any advice?

Specifically, my wife and I were trying to do an ironman run, we got to upper calrath and then I left for work, when we loaded back in my wife was back at abandoned redcopse, yet I'm still at upper calrath. I looked into how we can get our shared progression to work and we have to kill main bosses, is this just beacon bosses or is it even the named bosses? Not even fextra is too helpful with this so thanks in advance for any help.