ABANDONED. Sci-fi book about a house and an older couple that have to solve some mysteries/problems

[Physarium]

Hello everyone,

I am looking for a science fiction book about an older couple and a house. There is also a younger person, but I do not remember the exact age, probably a teenager.

They are in a house and they have to solve some mysteries/problems. There is a counter< i believe going up from 1 to 10 after one mystery of the house is solved.

On the end I think they are going to become younger (or in better health, I do nor remember exactly) and I think it was done by aliens.

I also remember that more or less at the beginning of the book there was something said about the sleeping patterns or the older couple: that one likes to get up early and the other likes to go to sleep late and that gives them some time to do whatever they like.

I would greatly appreciate any help.

[Kris]

Physarium, what year did you read this book?

Is it for young adults/teens or older adults?

How old is the older couple (40s, 60s, 80s, etc.)?

Are the couple and teenager related (e.g., grandchild)?

[Physarium]

I believe I read it a few years ago, probably as an e-book. The couple is definitely older that in their 40s, probably 60s or 70s, the teenager might be related, but I would not bet my money on it. I do not know whether to classify it for YA or older adults, I would say that it was more of YA book.

[Juels]

Maybe THE MYSTERY OF DARKSON HOUSE by Marcus Clark?

[Physarium]

Unfortunately, it is not that book.

[Physarium]

I have also remembered two things, although the picture is not very clear in my head:

1. the younger protagonist (probably) had to go through/squeeze through to solve one secret

2. they have discovered probably another dimension with a strange forest(?)

if that helps someone to find the title, it would be great

[Lobstergirl, au gratin]

Physarium, are you still looking for this or did you find it?

[Physarium]

Still looking, but I nearly gave up hope :-(

[0possum]

I read this a very long time ago and I can't remember if there are numbered mysteries in it but your query did bring it to mind.
Realty Check

[Kris]

No response, moving to Abandoned folder.

Physarium (OP) was last active on the site in October 2019.