You just need to put your landline base unit under the stairs next to the hub behind the door and buy a satelite charger for your model of phone then you can put the handset anywhere you want.
10 is a bizarre frequency to use, it will cause interference, you really should only use 1 6 and 11.https://www.intel.com/content/www/us/en/support/articles/000058989/wireless/intel-killer-wi-fi-products.html#:~:text=On%20the%202.4%20GHz%20band,on%20...