Honeymoons with destination spots

@Telmarina If the second sim is part of your household, you can just use the "bring sim to this lot" button on the sim portrait to bring them to the secret lot once the first sim is there.

Here are two of my sims in Forgotten Grotto. I've also done this in Sylvan Glade and the Deep Woods.

https://i.postimg.cc/762rPHqv/588-Okay-You-were-right.jpg

If the second sim is not part of your household, you could temporarily move them in via Manage Households for this trip, and then move them back out after the sims leave the secret lot. I do that a lot for story reasons.

Edit - I think there is even a "travel with" option on Deep Woods if the sims are grouped. I can't remember about the others. But I definitely have done it with the "bring to lot" option for family members.