Why does my iphone 5 keep dropping/ crashing my Wi-Fi?

Ok so i got my tmobile iphone 5 on the 12th and so did my sister the same day. Ever since then my Wi-Fi network is going haywire.

now when i'm on my network alone (sister iphone 5 not connected to network) my Wi-Fi works flawlessly. Though the bad part starts when me and my sister are home at the same time with both our iphone 5's connected.

i can't use any data heavy apps otherwise our whole network crashes and by crash i do mean the fact that every device in the house is kicked off and you have to wait five minutes for the Wi-Fi to come back. This happens as soon as i start using the Wi-Fi for apps like youtube or netflix more than just having the phone on stanby with it simply connected to Wi-Fi doing nothing.

like i said there are no problems when my iphone is the only iphone on the network.

i'm already on a replacement phone so i don't want to call for another replacement if the phone isn't the issue.

also the router we have is a linksys tmobile router WRT45G with WPA personal security.

when the problem occurs at the time there are usually only 5-6 devices on the network including the phones and also an xbox 360, ipad 3, and occasionally a laptop or pc. This problem never occurred when both me and my sister had samsung galaxy s 3's.

also my iphone 5 is currently running 6.1.2 while my sister is running 6.1.3
my previous phone was 6.1.3.

Please Help!

Added (1). Scratch tht the router is a tmobile WRTU54G i believe.

Try to update your router's firmware. It sounds like there's something wrong with your router… You should be able to put as much stress as you want on it without it crashing. I personally hate Apple and all their products they push out. But the problem lies within either your router or your iPhone… Also update your iPhone if you can.

If you're not having any problems when it's just your iPhone on the wi-fi network, it sounds like it's your sister's phone that's the issue, not yours.

My first guess would be a rogue app that's either trying to consume too much bandwidth, or that's doing something your wi-fi setup doesn't permit.

If it were me, I'd restore the phone to factory settings and see if it breaks your wi-fi again. If it doesn't, reinstall the apps one at a time until something goes haywire.

My second guess would be out of date router firmware.

Either your Wi-Fi sucks or the phone is having problems.