for gaming i really wouldnt use wifi especially through 3 walls, ideally you want either wired ethernet cat5 or cat6 OR at a push you could use Ethernet home plugs
In your parents home you may not want to be pulling carpets up for the cable so the homeplugs may be the best option, i bought some a while ago for my son and they work quite well, he played cod 4/5 for a while using them and never had any issues with ping or drop outs