Ping refers to network latency, i.e. the time it takes for one packet to reach its destination (and back). This time inherently depends on two factors:
- The time it takes to travel over the medium (i.e. over the air, fibre and other cables)
- The time it takes to process the packet (in every router there is on the way, that could be quite a few)
This however has nothing to do with bandwidth (or "throughput"), i.e. the amount of data that can be pushed through in a given timespan. This depends on the following factors:
- The physical transmission rate of the weakest member (e.g. your WiFi)
- Additionally: Bandwidth caps by the ISP or traffic shaping
- Lost data that needs to be sent again due to lossy channels (e.g. WiFi, 3G, etc.)
Because of that, it does not matter whether there are 5 other machines in your network or your PlayStation is the only one. It also wouldn't really matter if the other clients would download at a really high bit rate. Note that playing games does not involve so much traffic as it involves keeping latency low.
Any decent router for home usage will be capable of processing the data fast enough. So even if you were able to get the fastest router there is, you would only see a marginal benefit. This is because the ping time you experience is the accumulated ping time from your PlayStation to the game server you are playing on.
So if that game server happens to be a thousand miles away, that means your data has to eventually go through several routers, where each router inspects the packets being sent and forwards them. This takes time, and it will add up, so that in the end, you have a high ping rate.
Summarizing: If your other computers experience the same latency (ping time) as the PlayStation, there is nothing you can do. You will have to either blame your ISP for that, or the game server that is too far away.