Wireless Network Setup for public

Hello to you.
I have a little problem whitch I wish to share with you.

I have a server with 3 network cards and smoothwall firewall installed.
One network card - modem
second one - office network
third one - public wireless

I have just two Wireless AP and they cover the whole area needed.
These little routers (10euro each?)

(WA-2204A) Wireless broadband router

I must admit I underestimated a value of having a proper AP but maybe my problem is not this box related please advise here is what is happening :

One Router is connected through Ethernet to Blackbox, second blackbox due to it's remote nature is connected via WDS, wirelessly associated with First one.

If I add about 6 clients to the internet.... it's a nightmare.

Pings to 4.2.2.2 are about 4000ms, 2000ms, and dozens of lost packages.

When I'm only one using the internet, It's fine.. it drops maybe once or twice, but the ping is 40ms max the same as through the wire.

I installed extra strong antennas and measured a signal ( it was weak before) but now, The signal is strong. about -30 -40 db, but there is no difference with connectivity , it is TERRIBLE, it's slow, it drops etc.

My question is it a router problem ?

What Equipment do you use in your places ? I really want to cover one big office with wireless network , 2-3 AP's max, and there is no chance to connect those AP's via cable.. only one can be connected I'm afraid.

Is that going to suffer ? I'm aiming for MAX 15 concurrent laptops connected at the same time this is complete maximum.

(WA-2204A) Wireless broadband router
Obviously doesn't do the trick.. I recon it's this box , but.. maybe because wireless is half-duplex, it must be like that..

How people do it then? If I go to open Internet access points It just works flawlessly with many people connected..

Could anyone provide good advise ?

Thank you very much

But, the problem is with a connection to the internet.