Of course. Whether WIRED or Wireless, they all share the same ISP don't they? The Wired person has the ability to really sux the air out of everybody if you let him. Implement QOS, or SQM like THIS video, for a fairer and harmonious household.
agree it's more of a bandwidth problem than a wifi problem, 6 clients should be no problem for a typical home router.
True story, when we visit my parents a while back that pushed their network to almost a dozen clients and we had big problems on their old 5/2 plan (5MBPS up, and 2MBPS down). In the end the only solution was to upgrade to a 25/25 plan, all problems went away.