
NewLavi is a random kid from the bookman clan. I think Lavi is just an inherited name like Bookman is.
OGAllen seemed like a prev Order member or some soldier (we dont know much about him yet or why he agreed to the contract).
The son of the current bookman is OGLavi and NewAllen is carrying his soul so maybe they count as relatives?

There can only be one Bookman alive and One Lavi. The positions are chosen at birth.
Bookman is the current holder of the job. OG Lavi was born to be the next Bookman. He disappeared along with Nea and Allen on their journey (His job is to record history so it's not exactly like he abandoned his role).
The Current Redhead Lavi we know could only be born because OG Lavi "died". And that is how the Bookman clan knew OG Lavi is dead. Because a new Bookman heir was born.

In Chapter 251, The Zoogle Antique Shop, it is explained that there is a Clan named the Zoogles. The Zoogles are made up of Humans and Non Humans. They fight on both sides of the war, recording everything that happens. They exist to record history and serve Bookman. Bookman is the main recorder of history and controls the rest of the Zoogles.
To become Bookman, you must be born with the "Mark". The current Bookman should have long retired and the OG Lavi was the inheritor born with the mark of the new Bookman. However OG Lavi disappeared with Allen on a Journey somewhere.
When OG Lavi merged with Allen, he "died". This triggered the current red haired Lavi we know to be born with the new mark of Bookman.
It's likely OG Lavi and Bookman are not father and son but they did share a close bond as teach and student. The father title is more honorary. Much like how current Lavi is not related to Bookman but calls him grandpa.
So to summarize, OGNea was friends with OGLavi and made a host contract with OGAllen. OGNea gets killed by OGEarl who also tries to possess OGMana. OGLavi and OGAllen got merged after Acro attacked. OGLavi used his life to save OGAllen and OGAllen's body got mini. Acro erased OGAllen's memory and he became Red. Red meets OGMana with dog Allen at the circus but he has no memories of being Earl. OGMana names Red as newAllen. Acro causes OGMana and newAllen to lose even more memories. Yesrs later, OGMana dies and newAllen summons OGEarl and gets his akuma eye. OGEarl and OGMana finally combine into NewEarl. Years later, newAllen meets NewLavi and now newAllen is becoming OGNea again.
Is this right