try this solution http://www.tp-link.com/en/article/?faqid=281 and change the Channel on the router.

Do the devices support 5GHz too? how many devices are there connected to the router?

change another web browser.

i could not such configuration. i think you can change the password to secure the admin access.

you have put the iPad's IP address in the DMZ? Have you put the iPhone's IP address in the DMZ too?

where did you get the username and password? a) change the WAN connection type to Dynamic IP, by Network -> WAN on the webpage b) restart the modem and router If the internet is not working, as cora...