Unless your Cristec Nemo 25 charger has a lithium battery setting it will not be suitable for charging LiFePO4 batteries as it could damage them.
Re the alternator the lithium batteries will take as much current as the alternator will produce which they are not designed to do for any length of time and will probably seriously overheat. In my set up the alternator is connected to the engine battery and the LiFePO4 battery is charged via a DC-DC charger. I have a Victron Orion 30amp dc-dc charger which is probably the maximum for my 60 amp alternator. It works well but these chargers do get very hot. I have had to mount it on an aluminium base to act as as an extra heat sink and also install a 12v cooling fan. This keeps the temperature down to a reasonable 40-45c under most conditions.
Hope this is helpful