I've read a number of threads that say this LTW won't complete, even when you have two of all the required pets, including the minor ones.
I'm having the same trouble with it, and wondered if there's a way to trigger the LTW to complete using a NRaas mod?

I'm trying to have my sim catch the minor pets herself now, as I read a walkthrough at Carl's Forum that indicated a cat could catch some of the minor pets hunting, so I tried that too, but only for some of them, and then I stocked the rest of the terrariums, which didn't work.

And she didn't adopt all the pets herself either, I used MC to add one of the horses and her boyfriend, his dog and her four pups.
So I'm wondering if that's part of the issue too.

Does anyone know if the sim with the Ark Builder LTW actually needs to be the one to adopt all the pets and catch them?
Or if the major pets need to be male and female and not related?

Even after catching all the minor pets herself, it still wouldn't complete.

I didn't want to give up the 5 pets they already had, just to see if actually adopting 5 more would trigger it, so I gave up on it and switched her LTW to Culinary Librarian, something I could have her complete quickly, before her child was born.

I set up the main family so they wouldn't age or have anything momentous happen while I was gone, but I didn't want to be away from them any longer than I was, especially as the main point was to have her complete her LTW, since we had all those pets around.

But I've got multiple saves, so I can go back in and save one under her own game and play test that one for this LTW.

Not sure when that will happen, but I'll update this post if I find out anything.

I was told it was better to do this one with a single sim. I have tried it in the past with the mother in the family and she adopted all the pets or found them and it didn't work. I don't play with just one sim so I've not tried it again. Good luck.

Thanks for sharing your experience bekkasan.

I thought maybe it was because my sim with the LTW hadn't actually adopted all of the main pets, with your information, it sounds like the Ark Builder LTW is just glitched, and completes, or doesn't, randomly.

Quite disappointing after so many players putting so much effort into it.

I wasn't one of the many that spent weeks or a sim's entire lifetime trying to complete it, but it was still disappointing to have to change her LTW when the whole purpose of switching active families was so she could complete this specific one.

I could have had her do the catch 20 minor pets in the main house before she left quite easily, or even the culinary librarian, or one of the skill based ones, but I wanted the originally horses and cat to be with her, the animal lover.

Next time I'll do the research prior to setting up such a thankless task.