Solution, hardener and metal required to cast key duplicates
From the video, the material looks like some kind of silicone. There aren't many other materials that have that translucent elastomeric quality. If that's the case, the larger of the two mould solutions will be mostly some kind of silane precursor such as SiOH. The second part will contain the catalyst for the polymerization. Depending on the exact chemistry used it could be perhaps tin-based. My guess for the "hardener" is that it's simply more catalyst. Two part silicones with longer working lives are more common than very rapid cure ones so adding more/stronger catalyst as the third part may be just to make it cure quickly. Many silicones can withstand temperatures of 200+ °C.

As for the low melting point alloy, there are a number of things it could be. Given that the application is keymaking and people touch keys with their hands, I hope it's safe to assume that the alloy doesn't contain lead or cadmium. The video says its melting point is around 90 °C. The two closest common alloys without toxic metals are 58% Bi, 42% Sn @ 132 °C and 66.3% In and 33.7% Bi @ 72 °C, from the wikipedia page on fusible alloys, so it's likely some alloy with similar composition to one of these. Bismuth and tin are far cheaper than indium, so it wouldn't surprise me if the alloy was some mixture of those two elements.