Audio-Technica - ATW-3255

You've not really mentioned your budget, but it sounds like you're looking at the entry level gear (xr18) so lets go it's not huge. Unfortunately I don't think you're going to get anything that has 12 outs (6 stereo mixes) in any kind of budget, the cheapest options I'm aware of that would give you that really are the X32 (full desk option), or something like the X32/M32C rack (only has 8 outs) and an S32/DL32 stagebox to access the extra I/O. If budget is a concern I'd really look at your requirements and think what's a must have vs what's a nice to have, or can be pushed into later down the line. Me personally, I'm running a Soundcraft UI24r as I just had it laying around. I've also used an X32 (rack and full desk) and an X18r, each with their own use cases and pros/cons. I started using the Xvive u4 IEMs and just swapped these out for ATW3255 units as my band is doing bigger shows in more central venues (though I never really had any issues with the xvives). My point being, unless you're already a big touring act, your rig will likely grow with the band, and if the band doesn't grow, you're not out thousands or tens of thousands of $$$

In the five-piece band I'm in with we play bars and small venues (typically 200ppl or less). We have a setup like you're talking about - MR18, passive split for all inputs, 3 people on wired iem and 2 of us on an ATW3255 (all mono). Everyone runs the app on the phone to mix their own ears and it works great. We also record the individual tracks during the show(which I "mix" later). Currently we have 1 input and 1 aux out free, so while it's serving our needs, we'll need to upgrade if we expand any more. About half the gigs we get we need/want to bring the subs and tops and run sound from our setup. We all have day jobs/family commitments so time/convenience is important to us. I will probably pick up a wing rack in the next year which will be all we'll ever want/need. Quick note, I used the Xvive iem for a short amount of time but ran into issues at one venue where it interfered with their lighting setup. Also had some issues at a gig with ~300ppl.  I love the Atw3255, it's overkill for what we need but has been rock solid with tons of bandwidth for the price.