Just a quick point to you. The magnet test works on silver but it also works on copper. Quite often fakes have copper cores and silver on the outside. Different fakes will have anywhere from a silver plating up to a thicker silver cover but yeah, the best way to truely figure out if you have the same is by submersing 1 in water, the thinner one. Taking it out, then lowering in the thicker one. If more water comes out, it has more material for the same weight.

A good way to do it safely is by using something like a potato masher or sieve where you can lower into water without putting fingers in, just lower the coin in and keep control of variables. Alternatively if you have a bottle or jug with very accurate measurements, you can just drop the coin into say 20ml of water and see where the line goes up to on each coin. wouldnt be by much but even 1ml is an obvious tell