It is likely due to interference. Download the free wireless analyzer inSSIDer from
HERE and install and run it on your computer. Then look under the network tab and see what signal strength you get. Then check where the others use their computers and see what they get. If it is a much better signal than yours, that will give you an answer.
You could also just need a radio channel change if you find other channels are on your home router channel.
Is your router both 2.4 and 5GHz capable?