Is it a good idea/useful to use two Anti-virus apps on Android? Is it a waste to load two anti-virus apps on your mobile? Are two AV apps more effective than one?
No. I'll even go to the extent of saying using an Antivirus is of no use if you only install apps from Google Play.

But if you install apps from third party sources (i.e APKs, etc.), using an antivirus might actually make sense. But using 2 AVs doesn't make sense in any scenario imho.