1. Don't offer any substantial help. a) Tell them you're not an audio engineer and just do not have the proper experience or expertise in ANALOG audio or mixing audio. b) You are willing to help, but you're going to have to consult an outside source (i.e. call Sweetwater and ask them for the most basic and cheapest setup for your need) and neither you nor your staff are qualified to do anything except connect, turn on, and verify that it works.
2. Don't get an XLR Y cable. XLR should only be used for mono, it's a balanced signal. Your el cheapo option has a 1/4" mono output jack. Use a 1/8" to 1/4" mono plug adapter. You could also use the 1/4" stereo headphone jack.
3. Then use a 1/8" cable to a 1/8" mic lightning adapter, something like this b/c it supports charging as well.
4. Pan all audio to the Left channel. Setup the streaming software to take only mono audio.
5. Mark all the optimum settings on the board w/ painters tape indicating the "best" position for sliders and knobs. Label the cables and mics to corresponding input channels.
6. Write clear and terse instructions on setting everything up, including pictures.

The above setup is Mics->Analog Mixer->Left out 1/4->1/4 to 1/8 adapter->1/8" cable->Lighting Mic adapter->iPad.

OR get that Polycom A/V w/ Soundbar, b/c it's the bees knees and will plug right into a laptop and take care of everything in a under $1k package and makes setup and teardown dead simple.