Combine multiple Google sheets that can keep updating

Okay, so I think, no one seems to have exactly the same problem as I do...

I have an app writing automatically my health data into a google sheet.It does so in three different sheets inside the one file.Column A is always the date.Now, I'd would like to have a master sheet, that combines this data.

Like this:

SHEET1:

SHEET 2:

RESULT:

So in essence, I'd like to sort by date and combine the values from the two sheets into one line so there is one date per day.Is that even possible?

I've tried different queries and IMPORTRANGEs, but to no avail.I am a sheets-newbie, though...

Any help appreciated!