I was actually looking at some Celtic coins earlier and saw one very similar to the first one, but with more detail on both sides. The second one I do not really know anything about. Also I found something for you on the difference between tetradrachm and drachm - The drachm is about 18 mm wide and weighs about 4.2 grams of silver (size of a penny). The tetradrachm size varies according to when and where it was minted but ranges from 25-40 mm wide and weighs 17.2 grams of silver (larger than a quarter). I am not 100% sure about that because I found it online but if it is right that would mean its closer to a tetradrachm size.