Welcome to the S&W Forum. Yours is a somewhat typical entry here, the finding of a family heirloom and wondering just what it is, followed by all sorts of welcoming, advice, and sometimes offers to buy (of course.). You've already gotten a pretty good run down on what the gun is, so I'll speculate a little just for fun. It looks like your grandfather did what thousands of GIs North and South of the Border did... bring back a souvenir from the War, then stash it away and forget about it. I'm sure it had some special meaning to him, but perhaps your grandmother said something like "I don't want that dangerous thing around the children" so it ended up hidden away in the barn and forgotten. Unfortunately in the meanwhile your government has taken on some rather misinformed ideas about firearms and their ownership, so a few discrete (and perhaps anonymous) inquiries about its possession might be wise. I hope you will be able to to shoot it, as it is not only a neat family relic but a good, solid firearm in its own right. Enjoy it.
BTW, in recent years that Enfield bayonet has taken on a bit of value of its own. You might check with a militaria forum about it. Be ready to discuss length, blade markings, handle material and style, etc,etc. Those edged weapons types are as fanatic in their own way as we are!
Again, welcome to the forum and I hope you will both visit us again and enjoy your unexpected "inheritance."
Froggie