okay, thanks everyone for your help, but i still haven't solved it. probably my inexperience has to do with it too, but that's why we are here
i do know that getting relays to work with pi is tricky, because pi only provides 3.3V. thats why im doing it JD-VCC way... because then i think it is suppose to be easier because JD-VCC provides 5V for switching of relays.
here is what i tried now...
the battery way, 2xAA batteries, aprox 3.2V, if i connect red to vcc and gnd to in1 or in2, etc... red status light on relay turns on. And then if i connect external 5V supply to JDvcc and gnd, relay switches on, based on which input pin i touch with ground wire of batteries. So ground wire of 3.2V batteries is switching relays on/off
Now regarding connecting ground of pi zero to relays... I found multiple sources saying this:
Now, let's look at how to connect the relay board so it is really isolated. Notice that board has a jumper between "Vcc" and "JD-Vcc". Remove it. For complete optical isolation, connect "Vcc" to Arduino +5 volts but do NOT connect Arduino Ground. Connect your Arduino Digital Output pins to "IN0", "IN1" etc. Connect a separate +5 supply to "JD-Vcc" and board Gnd. This will supply power to the transistor drivers and relay coils. Look at the diagram above. Only the part to the left of the small blue arrows is connected to Arduino.
The thing is, when i was messing around with arduinos and relays one year ago, i had this exact setup going on... JD-VCC and GND... but arduino only had 5v pin and in1,.. pins installed, no GND. now one year later with pi zero i cant get it to work
and i tried using multi meter with continuity mode, and GND pins on relay board are definitely connected, meaning that if i also connect pi zero to gnd pin on relay board, then pi zero will not be completely isolated from relays anymore right?
what am i trying to achieve with these relays? its a simple PI bartender where i will use 8 peristaltic pumps to pump liquid into glass. Thats why i want isolated relay board, and external power supply to relay board to protect PI from spikes in pumps etc...
regarding wifi relays... that seems unnecessarily complicated and would add quite a bit of cost if i would buy premade ones... im trying to keep costs down and 3d print parts etc... and its gonna be opensource etc... for other people to replicate, so cost is a factor here... wifi relays will be last resort...
This sticky explains why : https://www.raspberrypi.org/forums/view
The simple answer is to use a ULN2803A between the pi gpio and the relay board, if you relay board is active low
using several 74HC125 if the relay board is active high.
i've seen that sticky, but its not really written for beginners lol, third of the stuff that is said in there doesn't make sense to me yet... and sadly i dont have either ULN2803A or 74HC125 right now with me... i do not yet understand how these weird spidery transistors work lol, i have yet to dive down that learning hole...
on a plus note... my A8 3D printer just arrived... so even if relays aint working right now, im as happy as i can be right now lol. it feels like Christmas came early