I don't know which satellite(s) you have (I assume RBS50, but correct me if I'm wrong). If I'm right, you have the ability to run a wired backhaul (run an ethernet cable from the router to one, or both, satellites; or from one satellite to the other; or from the router to one satellite, and from that satellite to the other satellite), and then place the satellites in better locations that help you eliminate the coverage gaps you're experiencing.
You could also just try placing the satellites in different locations in your home. You might not be able to eliminate your dead spots that way, but you might be able to put them in less inconvenient places. If you have a guest bedroom with great coverage, but it's typically empty, you might be better off rearranging your satellites, letting that room be in a dead spot so you can get better coverage in, say, your kitchen, bedroom, or wherever you commonly spend time.
Even something as simple as changing which direction the router or satellites are facing, putting them on a different shelf, etc, could improve things for you. Closer to the floor might cause there to be more obstacles for the signal, since a lot of furniture and fixtures are within three feet/one meter up fom the floor (sofas, chests, recliners, a lot of cabinetry, tubs, sinks, appliances, etc).
So maybe, first, experiment with how far up from the floor things are, and which direction they're facing. If that doesn't impvore things, try moving the satellites to different rooms to see if you get better coverage that way. If that still doesn't solve things, try running (a) wired backhaul(s) so you can get more distance between the various APs.
Also, sometimes people experience issues with devices not connecting to the nearest AP. Eg, if your streaming device is closer to the satellite than the router, but is connected to the router, it will have a weaker signal and lower bandwidth than if it connected to the closer satellite. If it's a mobile device, like a laptop or tablet, it may not hand off properly to the nearest AP, depending on how old it is and which wireless protocols it supports. Sometimes, just rebooting a device will cause it to connect to a better AP. Or even turning off the distal AP, forcing the device to connect to the proximal one, and turning back on the distal one again. Also depending on the age of the device, it may just be that it can't fully take advantage of the Orbi. Your Orbi is 802.11ac/Wifi 5, but if your other device is only 802.11n (Wifi 4), or worse, 802.11g (Wifi 3), you'll always be limited to the performance of the slower device, no matter your AP placement, how many APs you have, etc.
