Ran boat last week with no issues. The marine mechanics then took the boat to clean the engine compartment up and do oil changes. I go to put the boat in and it won’t start. Boat has power everywhere else. Batteries have been checked. There is voltage going to the starters. No voltage at the ignitions. There are unmarked fuses everywhere, and we have checked them all, and everything looks fine.

any suggestions? Seems to coincidental that the service center had it after it worked fine and now it doesn’t.

Not at all being condescending, make sure shifters are in neutral and the kill switch is in the correct position.
Now that I think about it, I think it will still crank whichever way the kill switch is.

We tried the kill switch and checked that. Whatever it is, it has to be something that is common to both engines. And no worries about being condescending... I am at a loss at this point. I’m also the exact opposite to a mechanic. Lol. I just know it’s something probably really easy once you find it.

I agree with the something common to both engines.
Did you check the continuity of the kill switch?
Reset all your relays?
Any relays on your engines?

Do gauges lite up when key is turned ON?

If they do and it just won't crank then it's the yellow/Red wire start circuit. Key, neutral safety, slave relay

If gauges do not turn ON, then Red/Purple and 20amp ignition fuse/breaker, kill switch

Assuming outdrives

Ditto on the 20 A fuse to the keg ig switches. Also, under the rear seat, your model may have 2 circuit breakers, either 40 or 20 A, they may have been tripped.