Why not hold the vigil in Malta? That makes more sense than going to Ireland! Oh wait, I think I know why...
It seems to me that whether or not they're guilty, or whether or not they know where Maddy really is, that it'd be in their best interest to go to Malta. Even if they know she's not there because they're being completely weird (in my opinion, of course), why not go?
If they want attention, then going to Malta and having those sightings discounted would give them more attention as "oh, those poor parents.. they went and held a vigil, and their daughter wasn't there... it was some other child!" type deal. They come off as very much enjoying attention. Rather than shooing the public away so they can handle their sadness, it seems they would rather walk right into our livingroom and have tea with me this afternoon. I'll be having peach tea, btw.
Unless... what about this scenario.. my brain is hot today!
This is all coming from the What-If Machine stored in my brain: What if... it is Maddy. What if... they loaned her out that night for... whatever traumatizing purposes may have happened. The ones that were um.. with her.. decided to keep her. Explaining the "they took her" comment. It's why she left the twins, knowing whoever it was that was with Maddy wasn't interested in the other babies since they were already long gone. So what if it is Maddy in Malta with her... "borrower", perhaps they don't really want this little lady back? Or perhaps it's simply that it's all part of the loan, and they didn't realize it'd get so much attention, so they can't go get her until the whole ordeal is done. They couldn't have possibly said nothing that night, people will notice a child is gone and if the parents don't react first, that brings more questions. So she reacted, but did it all wrong.
What kind of parent could admit, world wild, that they loaned their child out and have to wait until the rental time is over like she's some old library book? Maybe they still get payments for her, but the payments won't arrive until the attention has faded away a bit and the fact that it's not is making them flustered, angry, annoyed with the world, with each other, with things in general. I hope someone in Malta or perhaps the next destination since I thought I read something about a boat and a man, will take the child to an embassy and get her safe. I dislike the thought of her going back to that house though, she needs a new caring family.
In my opinion, since it's Earth, anything is possible as long as there are humans here.