Hello Kat,
first, I'd like to say that I respect you a lot for fighting for your right to see your children. I've been the child of divorced parents myself and I think it's very important for the kids to have both their father and mother around, if alone to let them feel that they haven't been a reason for the divorce.
You even more have my respect for how much thought you put into caring for your girls. And while I don't think that video games and movies are such a bad thing every now and then, I'd suggest to you that you should have little fear of doing something that you have already done. I can say for sure that whenever I visited my father, what I enjoyed most was going out for a walk in the forests with him and we did it a lot. (And it is to this day one of the activities I enjoy most with him!) It's also the most memorable thing we did, because my father enjoyed it as much as I did, it was something we could share in, regularly, and that only strengthened our bonds.
So, naturally I'd suggest you could simply go out with your girls, watch the birds, insects and stuff, if you feel like, take a nature guide with you, try to identify what you've seen or do so once you're back. Make sure that your little girl doesn't have to walk too far. ^,^ Other than that, let them share in what you like to do and if you have the feeling they like it as well, build on that!
In regard to sleep, I can recommend warm milk with honey before going to bed, it helps sleeping soundly! Also, maybe you'd want to ask your girl why she's afraid of the dark and go monster hunting for her or whatever! All in all I'd recommend that you take action to make her feel comfy at night at your place as well, rather than going for the reaction route - and the night light was a really good idea there!
I wish you and your children all the best!
Nico