I wouldn't clear it for the goats, just let them loose (within a fence obviously) in it, once they are old enough and not on milk anymore. If you are getting them as kids now, they will still be on milk, and should only have ad lib hay and some concentrate (the type you want to feed them later on), and once you reduce the bottles to two a day you could also introduce other green stuff, well after the milk feeds though. I have had tummy upsets last year when my kids went out onto grass too soon after drinking milk.... its messy and upsetting.
For drying - willowherb, nettles (July onwards), pea and bean haulms (but mine are always full of mildew by the end of the season). Fresh branches during the summer.
Just being nosy - where are your GG's coming from? Both girls?
I am getting a female GG kid too, after my second year of all male GG kiddings I need to get another female to keep my breeding going...