Okay, the NodeMCU has an on board voltage regulator that takes the 5v supplied via either the USB socket or the Vin (sometimes labelled 5v) pin and converts it to the 3.3v needed by the NodeMCU, so you won’t damage it by putting 5V onto either of these pins.
However, if you try to power too many other devices, especially ones that draw a reasonable amount of current, from the 3.3v pins then you can burn-out the on board regulator.
The relay board will require a fairly large amount of current to pull the contacts on the relays closed - obviously twice as much for 2 relays at the same time, four times as much fir all 4 relays at the same time. This current peaks as the relay is activated, so if you ever activate all 4 relays at the same time you’ll get the peak current draw at that point.
The relays need a beefy 5v supply to cope with this. It can be the same power supply that powers the NodeMCU, provided it can deliver sufficient peak power, but the output from the PSU should be split into two, one branch going to the relay, the other going to the Vin/5v pin on the NodeMCU, and the negative wire also needs to be split - one to the GND on the relay board and the other to one of the GND pins on the NodeMCU.
Which pins you use for driving the NodeMCU is important. With the Sonoff, these are dictated by what the manufacturer has chosen to do, ad in some cases they use pins that aren’t recommended for normal use, but they get around this by designing the Sonoff circuit to cope with this. You may have to change your choice of pins to work with the relay circuitry that you have.
You should read this thread for more info:
I’d assumed from your earlier question that the relays weren’t working, but you’ve said:
so I’m a bit confused about where you are with your project.
Pete.