The Inquisitorius hunted down Jedi and other force-sensitive beings who were a potential threat to the Empire. We have seen many of them on assignment through a variety of media, most eventually meeting their demise. Here is a list of all the inquisitors who did not appear in Star Wars: Rebels and why they did not appear later to hunt down Kanan, Ezra and co.
Warning: Spoilers for Jedi: Fallen Order, Jedi: Survivor (this one is in a spoiler tag since the game is still pretty new), Obi-Wan (Show), Ashoka (Novel), Tales of the Jedi (Show), Darth Vader (Comic)
The Second Sister was seen in Jedi: Fallen Order as she took the lead in the hunt for Cal Kestis. He failure led to her death at the hands of Darth Vader in approx 14 BBY.
Nothing is known about him. The only reference is he was mentioned briefly in the Star Wars Encyclopedia.
The Third Sister is involved in the hunt for Obi-Wan Kenobi in Obi-Wan which takes place in 9 BBY. After betraying the Inquisitors and Darth Vader, she leaves to go off on her own. Her fate is unknown.
The Third Sister is involved in the hunt for Obi-Wan Kenobi in Obi-Wan which takes place in 9 BBY. Little is known about her after, however Rebel Lina Graf acquired her armor and used it to impersonate the Fourth Sister around 2 BBY.
Sixth Brother was the primary antagonist in the Ahsoka novel. He died in a duel with Ahsoka on Raada. Ahsoka used his kyber crystals to forge her white lightsabers.
The Ninth Sister was involved in the hunt for Cal Kestis.
In Jedi:Survivor she was killed by Cal in a duel in 9 BBY on Coruscant.
The Tenth Brother is seen in the Jedi of the Republic – Mace Windu and Darth Vader comics. He was killed by Purge Troopers in 18 BBY on Coruscant.
A masked Inquisitor was seen in Tales of the Jedi S1E6. It is unknown if he is supposed to be the Sixth Brother as the scenes have many parallels. He was killed by Ahsoka Tano.
A male Twi'lek inquisitor was seen in the Darth Vader comics. He was killed by Vader in 14 BBY on Coruscant.
Iskat Akaris was a female Inquisitor of unknown number from the Darth Vader comics. She was killed by Vader in 14 BBY on Coruscant.
An unknown female Inquisitor is mentioned in the Force and Destiny RPG Ghosts of Dathomir adventure book. She was killed by her nightsister apprentice at an unknown time. (I dont think this counts as canon but I thought I would include it)
Why did no other Inquisitors come to hunt after the crew in Rebels? Well most were dead. There is no indication of Inquisitors being replaced after death. So it's likely when the 5th and 8th Brothers, and 7th Sister meet their end, there were no more Inquisitors left. If there were, it's possible they were on other missions at the time.