You don’t need manual mode, and using manual inside is very very difficult
Use normal or sport but normal will be fine
The avata 2 has downward sensors so will stay in position when stationary below 10m
As said before you don’t need and will not get a good GPS position when indoors
As Sparky has said, no need for manual, AVATA 1 or 2 has bottom sensors, so as long as its not too dark it will hold position quite well, my workshop flights were all flown using the MC2, no manual flying as I don’t have the FPV RC yet…
Not manual. I think normal mode with an avata. Damned stable (albeit very slow lol)
I think that at the end of the day this whole discussion hinges on this:
You need to have a discussion with him and come to an agreement on exactly what he expects and exactly what you can deliver.
Is he thinking of something fairly simple with a couple of short clips panning around some rooms or past decorative features cut together with a shot sweeping over a glorious vista before descending and coming (just) inside the door?
You can do that with a Mini 4 Pro and a little practice (though, as you found when you tried it using your drone, if you want the kind of smooth results Ken Dono gets in the video @Hotrodspike posted earlier you’re going to need something handheld and ideally on a gimbal for the indoor footage).
Or has he been watching YouTube videos of drones swooping through an open door, zipping around corners, flying through a hole in the the middle of a bagel an attractive model is about to eat, before doing a barrel roll out of an open window and across the garden?
If that’s what he wants, the Mini 4 is very much the wrong drone for the job and you’d need an FPV, a lot of practice… and something bigger than a bagel.
Ok, Maybe an Avata 2 set back to beginner mode.
I have one, I just tried my house fly through, seems to work. sort of.
But a 360 camera would give a more stable video / pictures.
And you could probably push it through a bagel too! 
You might find this video of interest
He does a fly through with an Avata
@AlbionDrones @SparkyFPV
That is what I wanted to hear. Thank you for being informative and having patience with my lack of knowledge 
@JoeC
I agree. It was my first job of this kind so I got overwhelmed and just said yes to everything. It’s something I’ll have to learn from. When I submit the outside photos and videos I will ask him specifically what he wants.
Thank you mate