Weak/Variable Connection between our Macs and our WiFi router
When you added the NAS to the LAN did you move the router?  It's possible that even a very minor shift in the position of the router or the antenna could impact the shape of the signal zone.

You might try pairing up with your husband where one of you is in by the router and the other in key use-areas and recording signal strength based on the location, orientation and position of the router and router antennas. (don't know if this model has external antenna, if not rotating the router itself).

There are tools that can give you more detailed report on the signal strength, for instance you might want to download and install Kismac on your MacBook.  Kismac and similar tools can also give you some insight into what other networks might be interfering with your own.  If you see strong signals on the same channel that you are using you might consider moving your network to another channel.