Slow web interface, adding new wifi devices causes wifi to go down and more

I use multiple computers and devices.  We even replaced my wife's computer (which is the ethernet connected one) last week and it has the same issue (granted I can't try this on the R7000 anymore since I don't have it).  We use Windows Defender, no norton or anything.  I've also reformatted my main computer once and the problem has always been there.  Even things like the cell phones and the Nviida Shield which have no antivirus, just android on them, have connection issues.

When I hook up this old linksys router I have it works great wired and wireless.  The only reason I don't use it is because it's not as powerful and can't cover the whole house properly.  I will admit though, this house does seem bad for wifi as the old Linksys router used to be able to cover my old apartment.