How do I troubleshoot 2 light switches in the same box with 4 black (hot) wires?

Question

I opened up my bathroom light switch and fan box to replace the switches. The light is for overhead and the fan is a standard bathroom fan.

Inside the box I found 4 sets of wires (1 black, 1 white, 1 ground per set). After measuring the voltage of each black wire, I found all 4 to be hot. When I wired up the single pole switches (1 black per side of switch with all 4 neutrals pigtailed together), not only did the light and fan not work, several outlets downstream of this particular box did not work. When tested with a 3 light outlet tester, they presented with a “hot/ ground reverse” result. When I tested the voltage of the neutral line in the same outlet, I received a small voltage reading which coincides with a “hot/ground reverse” result.

I did not take a picture of how the switches were initially wired but all 4 hot lines were used and 1 line was strung across the 2 switches (not sure which terminals). The neutrals were all pigtailed together.

I’m not quite sure where to go from here.

Answer 1

So the neutrals were all pigtailed together and you didn't disconnect any of them, right?? So one black wire is your always hot and is strung across both switches. It is also connected to one of the black wires that feed the outlets that are not working. The remaining two black wires go to each switch to control the light and fan. Your job, should you choose to accept it, is to determine which wire is which by process of elimination, connecting wires two at a time and see what turns on or with a good meter. Naturally, you'll be turning off the breaker every time you touch in wires.