You can check https://trueofvamp.dreamful.org/ to see the timeline
Iirc they also posted the links to the stage play subtitles
But the main story is from TRUMP
Maybe you can watch TRUMP first, then go back to SPECTER and Grand Guignol to understand the characters better
Could you please give a spoiler what happend to Fra Gerhard? I couldn't find anything about his status in the manga and I love him in the anime. Will he die?
I'm not sure about Gerhard because I haven't found any stories about him after TRUMP. Let's see if later the author will give us an update on him and Dali.
Where to watch the play of this series and in what order???
I didn't know I was jumping into a deep rabbit hole