There are a variety of factors that cannot be accounted for with your inquiry. What specific Roku model device will you be purchasing? How far will these devices be from the router?
There honestly won't be an answer we can provide rather than you just purchasing the devices and seeing if they work in your intended setup and if you are not happy with how things are going, we would recommend returning the devices from where you purchased them.
You can probably get a preliminary reading by taking a phone or tablet that connects to your home wifi set up down to the new basement rooms and check whether they make a good wifi connection there.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X