building a 3S2P from scratch 18650s - how to charge?

suggestion: connect cells first to parallel (2 in parallel)

and then connect these 3 “packs” together in series

then use a balancing charger to charge them, such as for example:

you would also need a balancing connector

the problem with using the tp4056 boards to charge them is that I suspect the tp4056 might have common GND shared between the DC in and Batt charging terminals.
So if you would use those boards with one power supply, you would basically short all Batt- together.

Also note you should never charge Li batteries unattended. All the chargers above don’t have temperature control over battery.