Orbi cross floor penetration

You mention your new home is an apartment. One of the largest reasons for WiFi dropouts and sluggish performance is interference from other WiFi signals. I also recommend you do a WiFi scan (there are many smartphone apps available for this purpose) of your apartment. I also suggest you read this article regarding how WiFi handles interference: https://arstechnica.com/information-technology/2017/03/802-eleventy-what-a-deep-dive-into-why-wi-fi-kind-of-sucks/2/

As far as cross-floor penetration goes, the ideal situation is to have your router on the middle floor with the satellites on the 1st and 3rd floors (if 2 are necessary, as you never mention the size of your apartment). This will give you the fastest throughput and lowest latency with an ORBI. Of course, all of this is predicated on the type of construction in your building. ANY metal objects (rebar in concrete, metal mesh for stucco, kitchen applainces, etc.) will degrade any WiFi signals dramatically. It will take a bit of trial and error to find ideal locations for the router and satellites. A small change in distance between the router and satellite can have a BIG impact on signal strength so don't be afraid to move things just a few feet at a time. Good luck and keep us posted.