untxt and pstxt values are not set.It takes value only when you click on other button.You never did guiGetText when it clicks on rgbtn button.
Do like this
function getRegEdits()
untxt = guiGetText(uned)
pstxt = guiGetText(psed)
triggerServerEvent("register", root, untxt, pstxt)
end
addEventHandler("onClientGUIClick", rgbtn,getRegEdits)
function getEdits()
untxt = guiGetText(uned)
pstxt = guiGetText(psed)
triggerServerEvent("login", root, untxt, pstxt)
end) --REMOVE THIS BRACKET
remove bracket after end