As a brooch, it will be of minimal value or interest to coin collectors - it has far more value to you as a personal family souvenir. Trying to "Turn it back into a coin" by attempting to remove the brooch will not work; the coin has already been damaged when the brooch was attached. It will be worth more to a jewellery enthusiast, as a coin brooch, than it would be worth as a damaged coin to a coin collector.
It probably won't help your mood when we tell you that this coin, if it hadn't been turned into a brooch, would be worth several hundred dollars - possibly more, given that world coin prices are going crazy right now.
Here's the NGC database page for this coin. As-is, maybe $50 to $100. Minimum value $20 - that's the silver scrap value. Of course, part of the reason that undamaged coins are valuable, is that many of them were melted down - or turned into brooches (I have seen numerous Japanese yen that have had brooch mounts torn off them, so it seems to have been an unfortunately common fate).
Of course, if it hadn't been turned into a brooch, your ancestor probably wouldn't have kept it at all. So I guess we can't really complain.
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