How depends upon your iPad or iPhone connections.
You need a Line Output from your Mixer and feed that either directly or via an intermediary box to the iPhone connector, it is all about the available connection.
Google the kit and choose one to suit.
i.e. if the iPhone has a TRRS socket that is the easiest way and a simple adaptor cable will give the mono mike input.
The other way is to simply record all on your iPhone and capture the audio on a Tascam or Zoom audio recorder, this is the audio you will then use in the video. This will give by far the best audio quality and will be easiest to set up.
As for editing, how and what you use depends again on the age of your kit.
I’ve edited hundreds of hours of video and even quite a few on my iPhone but it is hard work. On my iPad and iPhone I use LumaFusion which is vastly superior to iMovie.
If you have a Mac then transferring the footage to said mac and using FCP will give the best results.
On a PC then Adobe Premiere is the de facto standard but costs whereas da Vinci Resolve is free for the basic version which is equal IMO to Premiere and yet still handles 4k.
If top quality is your goal forget using an iPhone and use a DSLR camera, still feed in Line Audio but the recording data rate and codec used will be vastly superior to that used in an iPhone, been there compared them. I record all video in 4k on my Panasonic DSLR, and have a Rode VideoMic Pro for ambient audio.
BTW I used to teach Video Editing as a sideline.
Good luck.
