Roku express comes with simple IR remote, which can't be change to a different address. It will control all other Roku that accept IR commands in its sight. IR signals can bounce off walls so it can control other Roku's in other rooms if the signal can reach. Remedy is to abandon the IR remotes from BOTH Rokus and replace BOTH with Roku Wifi Voice remotes. Which can be purchased separately. Cheapest is $20, there are two Voice remote with rechargeable batteries and other features for $30 a piece. This is your only remedy.
... or take physical measures to keep the infrared remote signals from bouncing between rooms.
