POD to the above--it can be easy to overthink these things and get oneself mixed up. (Which I might be about to do!)
My suggestion is to make it crystal clear what each person is invited to, and not mention to them the things that they aren't invited to. The only exception would be, people are going to notice if they're invited to a wedding event but not the actual wedding, so that might need to be explained, because sometimes people might be offended (you only wanted an engagement gift from me and I didn't get to see the wedding!) if they don't know the full story.
Let's say Aunt Myrtle lives in Hometown #1. What will she be invited to? The June engagement party for sure, since it takes place there. Not the July destination wedding. Will she get invitations to the early August reception in Hometown #2 and/or the late August open house in Current City, though it's unlikely she'll attend? So her invitation might be like, "You are cordially invited to Engagement Party..." and then you make sure she knows (either in print or verbally) that she won't be at the actual wedding, because it will be very small. Maybe this can be conveyed tactfully at the party where you see her and/or through the family grapevine. Then I think after the wedding, I would send her an "address card" stating the HC's names and address, perhaps announcing that the wedding has taken place, when, where, etc.. Even if nothing has changed (like they were living together in the same place before), that will be a chance for people to double-check their records and have the official word. I would try not to mention the reception and open house to her, if she won't be invited at all.
With four different events I think it could be confusing to people who hear about all the plans through the family grapevine but aren't actually invited to all of them, so I would just take pains to be very clear when issuing invitations, and don't give info like exact dates and locations to people who aren't invited to those events--not because they might be rude and show up, but just to avoid confusion, and things like people making big travel plans to attend something you really didn't intend for them to be at. Conversely, if you hope people can attend something that will involve travel, make that clear, with details, as soon as possible so they can plan.