For the splits you could use a simple 'Y', the mixers should be able to accept seeing phantom from the other mixer. But you may be better to use transformer splits with whichever mixer is most likely to always be in use with the mics on the direct output that passes phantom and the other mixer on an isolated output. Radial Engineering, ProCo, Whirlwind and others offer multiple channel mic splits, I personally prefer to use those with Jensen or Lundahl transformers. Another option is to use a split that allows inserting phantom at the split and a separate phantom power supply.
The council chamber and especially courtroom aspects may add some special considerations. For example, for the Council Chamber application you may want the council and audience seating as separate zones. You may also want to be able to mute the microphones for the audience but not for the recording.
If you are not familiar with courtroom system then that aspect can require numerous application specific considerations, especially if it is a jury courtroom. For example, you may have to support sidebars where the attorneys approach the bench. That means a sidebar mic at the bench to pick up the attorneys with that mic and the Judge's mic going to recording but not to the house. You may even want to send masking noise to the house and jury speakers during sidebars. You may want numerous zones (seating, well, jury, bench, etc.) so that you can mute and adjust volume separately for each zone. You may also want some way for the Judge or Clerk to control everything. And don't forget to address the Court Reporter if they have one or the possibility of their using an interpreter or remote interpretation services or even feeds to a Press area.
Interpretation and especially ALS are often critical components of Council Chamber and Courtroom audio systems. And because of the courtroom aspect they often have to be IR so that they cannot be picked up outside the room. Although wireless microphones are common for the Council Chamber use, for that same reason Courtrooms tend to avoid them unless they are IR or encrypted.
The mics over the seating are typically used for jury selection and/or entering pleas rather than during a trial and are primarily for for the Judge, Clerk and recording. I find that low profile, white, omni boundary mic such as an AKG PZM10 or C562 CM, Clock Audio C 007, Audio-Technica ES945 or Shure MX935 is often good for this application unless you have a high ceiling, in which case you might want to look at hanging choir mics to get them closer to the people speaking.
For both bench/council table in both courtrooms and council chambers I like to use small speakers mounted in desktop enclosures or integrated into the millwork. That allows each council member in that use or the Judge, Clerk, Bailiff, etc. in court use to adjust the volume of their own speaker. Overhead speakers can work but tend to cover more area than desired and often turn into a battle in terms of the desired volume.
Because of all the different zoning, muting, automixing, remote control, etc. that can be involved I typically use matrix DSP devices for courtrooms and council chambers.
