So here is my homebrew ultramarines successor chapter

Chapter name : Templars of justice Founding : 13th black founding Codex compliant chapter Chapter colors : White with gold accents Chapter symbol : A shield that has two lighting bolts on the top of the shield Successors of the Ultramarines Home planet of nexus primaris this a ring of five planets with the first one being a advanced militarized planet that most of the imperium praises and the other planets include a Forge world , knight house and two agricultural world

Templars of justice specialize in advance troop tactics, Defensive warfare and defense of guardsmen and civilians and close combat

Chapter master jaune is a very strong commander has been the only chapter master of the Templars of justice he uses MK8 armor and a Power sword , storm shield and a Bolter combi plasma

Chapter allies : Ultramarines, most Ultramarines successors , Crimson fist , Sons of Medusa , Blood angels , White Templars, Storm lords and Salamanders and Storm giants and deathwatch and Grey knights

Chapter that dislike the Templars of justice: mantis warriors, space sharks , dark angles, chaos , Xenos , marines malevolent

Chapters neutral to the temple of justice: Red scorpions , Imperial fist , black Templars, Angels of absolution , white scars , flesh tearers , celestial lions, blood ravens , raptors , iron ravens, Dragonspear and Dark krakens

Some lore : The Templars of justice were the last of the chapters to get primaries reinforcements and couldn’t come saves the 500 planets from the death guard thanks to being occupied by the orks and were forced to deal with a Ork waaa that attacked their home planet and where rescue by the nova marines , Genesis chapter , tome keepers , red scorpions and white Templars