Thanks for the hint. We were looking at everything we have in the house and we plain don't have ANYTHING large enough and at least "whitish". Weird household, I know, but that's what it is. We don't own the typical bedsheets.
I'll likely get some reasonable stands and white cloth or curtain, or whatever for next time. It's not too expensive and overall worth it.
Thanks for saying I got it right - took a while to dial in the exposure, positions, flash power in all places and as I had different flashes also the experimenting which one worked best where. In the end I just did with one 32" umbrella and two Yongnuo flashes triggered wirelessly. It wasn't hard, just took a while to dial in all the parameters.
Popup backgrounds are excellent and super easy to travel with
myriad color choices too