Slitherine

There are 5 factions that have claims on Constantinople every save but they do not own any region on map.
They will abandon claim on Constantionple if you gift them 1 region but they accept all regions you want to get rid of.

templars
hospitallers
iberian order
sword brethren
teutonic knights

Are there some events with those 5 factions and Constantinople and what is point of their claims on Constantinople?

Byzant is heretic to these holy orders.

They can very well get regions through military methods. I have seen saved games with the Templars with 50+ regions and large portions of the Holy Land.

You can hold them down, but it usually requires placing the Judean Liberation Army on permanent station in Judea.
As Byzant, Seljuqs and Fatimids its a doable job.
But you might want to either become friends with them or demand their claims in peace.