i may rehash some of what has been said.
where is the router location to respects of xbox and android?
rancher or multilevel house? how many levels, how long and is there anything like a refrigerator, washer, dryer, etc in the path from router to device?
what type of lights are in the house, i agree that some florescence and CFL's have caused issues
what is model of modem and router? are they separate devices or all-in-one?
is the router tucked behind anything or as high as it can be placed?
how old is the router? (if a couple years old and provided by isp they may switch it out to newer model...same with modem)
also if it is an older router do you have it right beside anything else wireless that might be a base (example cordless...