SOLVED. Children's fantasy series in a seaside town, with portal to a parallel dimension. [s]

[Aude]

I'm looking for a series of books published in the 1990s/early 2000s. The protagonist were children/teens living in a seaside town.

There was a portal leading to a parallel/alternate version of the town with darker, more fantastic aspects.

There was a castle looming above the town, and a lady lived there (witch? I seem to remember she had some sort of magical powers, and was a villain).

In one book the younger sibling of a male protagonist was sweeped away by the sea, and turned out to be held by a ghost in a lighthouse.

[Johanne]

Could it be Troubletwisters from 2011? It has some similar elements. I read it when it was first published, so I don´t remember all the details.

[Aude]

Thanks, but no, that's not it. I'm positive it was published at least a decade earlier.

[Aude]

Found it ! It's the Spooksville Series by Christopher Pike : https://www.goodreads.com/series/4969....