its very obvious the Cottage on DR and the mothers are one and the same. When Harry joins MS on the rock, which is in the same spot as the lighthouse, it allows them to travel to the outergates. Evidence the sleepers and the dreamers(outsiders wanting in) are one and the same?
The Mothers are powerful enough to port around basically wherever they want. Even in
Changes it seemed like Vadderung was powerful enough to make an item that opened a wormhole directly from Chichen Itza to Chicago. The Mothers can open a Way from their hut to, anywhere essentially. I don't think anyone can got to the Mother's place, or even find it, unless they
want it to be found. I don't think Harry really just stumbled upon them in SK, more like they manipulated the NN so Harry would find them.
Knowing the Merlin, it *could* be that he was just that well-connected that he got a shortcut on his island to see them, but it would be by their Will. Now I could see DR having a shortcut to the Outer Gates on it, that would be
awfully convenient.
Let's be real though, if there's any sure-fire Way to get to the Mother's place, it's to use a copy of *Who Framed Roger Rabbit*.