updating to LiFePo batteries

[pjstock]

I have started to do what I thought would be a simple exchange of my old GEL aux batteries for a pair of LiFePo
However, reading further it seems that I cannot leave the alternator connected directly to the LiFePo batteries.

I have the two LiFePo batteries, I have the 120v charger, I have a monitor/Shunt.

I presume I have to disconnect the alternator to aux battery connection
I also understand that I can install a DC to DC charger to charger (which I do not yet have) from the starter battery to the LiFePos
and, once again, my inexperience is causing me problems. (and it is not easy to find someone to help.)
I doni't even now what all the cables are for that are attached to my current aux batteries.

Has anyone done this?
and can advise?

(Or maybe I just keep looking for an experienced available professional)

Peter