what is the current firmware ? If they put US firmware in the Brazil website, which means we can use that firmware, i think. http://www.tp-link.com.br/download/TL-WDR3500.html#Firmware

here you are, http://www.tp-link.com/us/faq-1083.html

V1 means the hardware version and so it is ok to select v1 as there is only version for td-vg3631 http://www.tp-link.com.au/download/TD-VG3631.html#Firmware

found their sales contact, you can ask them for help. http://www.tp-link.fr/contact.html

both APs are connected to router by cable? what is the distance between them? you can setup ap mode on both units with same SSID and password, but different channel, 1 and 6 is better for roaming.

what does that mean?