Gee, this is a bit like that question "which camera should I buy?". Almost unanswerable. You have said what you want to shoot (good start) but not how much money you can spend. The standard 14-140mm zoom will cover the focal lengths you generally will want, but if your emphasis is on indoor shooting without extra lighting you might be wanting more aperture. This is where the question of money rears its head. You could go for a Zeiss 18mm prime f/1.4 .
Perhaps this is where confusion set in. Given the appropriate adapter you can use any of the huge range of still camera lenses on the market, including those bought second hand. Many of these you would have to use in full manual mode, so that asks "do you want full auto?". Do you need a zoom, or can adjust framing by changing subject distance? If the latter, then you can choose a wide aperture (f/1.4) of a suitable focal length for your work. The price of a good zoom lens of wide aperture will match a suite of prime lenses. Working indoors will bias your selection towards wide angle (short focal length), but wide angle is distorting of face CUs. A good portrait focal length for full frame 35mm is in the region 80-100mm, which is about 25-35 for the GH2.
And then there are questions about how you will set the camera up and the costs of those bits. You might start with the standard zoom lens and learn through experience where you want to take it.