I’ve been requesting for a true native multi-view player from Channels DVR with integrated EPG for a while now and still hoping someday that this feature will be integrated or as a separate player. Now that you're able to add custom M3U playlists you should be able to Live stream those IP cameras, IPTV, and TVE feeds in a multi-view mode.
Here’s a couple of options while we’re still waiting; CCTV Viewer (tvOS/iPadOS) & Surveil Stream (tvOS only)
I’ve been playing around with CCTV Viewer for a while now. This app was designed for viewing CCTV cameras but it works great with Channels DVR.
With CCTV Viewer you can create multiple groups and have up to 16 channels per group. I’ve created Entertainment group with 16 channels (4x4), Sports group with 9 channels (3x3), and News group with 4 channels (2x2). I think the 9 Channels multi-view (3x3) is the sweet spot. Once the groups are setup you can toggle between them on the fly.
CCTV Viewer has a builtin web management server for setting up the URL streams, export/import, MDM support, and it works on tvOS and iPadOS.
Both of these apps do need improvements and bug fixes but I can live with it for now.
Example one of the TVE channel (ESPN1) setting: http://YOURDVRIP:8089/devices/ANY/channels/6140/hls/master.m3u8?codec=copy