Frankly, the two on the right do not look authentic to me. The Bactrian one (far right) is very commonly faked, especially in Afghanistan, and there seems to be evidence of casting on this one. The Seleucid coin of Antiochos IV (second from right) looks very strangely damaged - I'm not sure if it's been in a fire, or if it's a poor quality cast. It should look something like
this. The picsd of the two coins on the left are too small to judge authenticity properly, but if they all came from the same place, then I'd be suspicious of all of them.
The German piece appears to also be a copy, this time of a gold 10 dukaten of the Austrian state of Schlick.
Compare with this example. Clearly, your piece is not made of gold, and also has the remnants of casting sprues or seams around the rim.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis