change the channel width to 40mhz and try different channel like 1 or 6. also try some suggestion mentioned in this link. http://www.tp-link.co.za/faq-468.html

8968 v4 support parental control but it only block website not programs. however, you can setup bandwidth control to limit his computer's download speed. you can refer to manual to set it up....

does this happen only with 5Ghz or both bands? are you able to login modem web management page when problem occurs? and when Wi-Fi is not available,are you still able to see it or it disappear? is...

if you don't want to control the internet access, it is better to disable firewall rules. this is actually access control not the true firewall.

when internet is not working,can you ping 8.8.8.8? if you do, then you can try manually dns.(DHCP--dhcp settings--primary dns server 8.8.8.8 and secondary dns server 8.8.4.4)

it is remote control enable? you can find it under device--device settings--remote control if you can not enable it, please try the firmware upgrade first.