Well, it would be very strange if your router only supported 5 wireless clients. It may only have a small number of wired LAN ports on the back, but most routers made in the last few years will support a large number of wireless clients. However, the more clients you have connected at the same time, the less bandwidth each one has, so the slower they'd all be.
10 devices total shouldn't be a problem assuming that they're not always all on at the same time.
This isn't meant to be a long term solution, but the darn security settings can often cause problems, particularly when certain devices only support specific settings. A good test (and only a test) would be to:
1. reset the router to factory configuration
2. Enable wireless, but do not set up WEP or WPA (leave it Open)
3. Fire up all the wireless devices and see if they can all connect to the router (play with them a bit to see what the network speed is like)
4. If that all worked, pick the least common denominator for band/security (for example, a Nintendo DS might only support Wireless G, and only WPA)
5. Re-enable the simplest security and start adding all the devices back one-at-a-time
If that works you can shoot for a higher level of security (WPA2 for example) and see what kind of luck you have.
Hope some of this makes sense and helps.
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