Renovating existing garden enclosure

[Muchelle]

Hi again, in my intro topic I wrote that me and my boyfriend have 'inherited' two 20yo hermanni and we're planning to move them to our apartment.
Alas, there are unexpected renovations to be done and we aren't sure we can safely bring them home before winter comes.
We have made arrangments to let them stay in the flowerbed that's always been their home until next spring: we can check daily on them and received permission to maintain and upgrade their current enclosure.
We already made it so that the two boys are separated for safety.

All of that out of the way, I've read around, consulted the safe plant list on thetortoisetable and would appreciate receiving some opinions about what we are about to do!

1. Soil: we think that the current substrate is a mixture of expanded clay, sand, flower soil (?? is this even a thing? I mean the soil used to repot plants). We're planning to mix in more soil to top up the existing one, that dries very easily, and to prevent mud from forming when it rains too hard; all rocks we could find have been moved and used to secure their homes, which are the two halves of a broken ceramic vase, firmly planted into the ground;
   
   
2. Moisture: we're thinking to use one of those watering cans with a shower head to sprinkle water where the sun hits and the soil keeps going hard; Their sleeping spots are set up so that the soil there never totally dries under there;
   
   
3. Greenery/extra food: I'd like to plant an hibiscus, maybe a boston fern or a snake plant + some other edible herbs (wheat, oat, taraxacum, cat grass...). My plan is to keep our plants of choice in some vases all around their enclosure for easy access and make it so that we can cut/serve (and so that we can move them when we'll be able to bring the boys home with us);
   
   
4. Enrichment: I want to try and plant some common yard grass or succulents in their barren enclosure, but these two bad boys are destroyers of worlds... I'm not sure they'll let it grow... do you have any tip?
   I'm also not a fan of tunnels or similar, the boys constantly have the choice to be out in the sun or in the shade. Is there anything else torts could enjoy that I am missing?
   
   
5. Comfort: we have added two nice big rough tiles where they can sunbathe, eat and do their nails on. Shallow water dishes have also been 'installed' in the soil. I've read about adding hay inside their sleeping spots, so I'm thinking to do that as well;
   
   
6. Health: their shells/nails/beaks look pretty good, is it recommended to add anyways a sepia bone? I'm afraid to be changing too much too fast and to cause damage... I've also noticed that many people soak torts every now and then in warm water: they never received this courtesy so we are not planning to do so, would it be a sensible decision?

I think that's all. Sorry for the loooong post ? We're n00bs and realized we're really nervous about this whole tortoise-care thing...