Hi. Good for you for doing this, but please be aware that Edinburgh Zoo is very, very hilly.
Best thing I can suggest is to go online and look at the map. Pick out the animals you and the kids really want to see. I'm disabled and really wanted to see the giraffes and zebras. Never managed it as they are right at the top of the hill. If the weather is hot it can be utterly exhausting. Pack light (I had a lot of water, packed lunches etc in my backpack and it really weighed me down) Allow a good few hours to get round with a couple of rests stops; packed lunch stop, ice cream stop.
I sort of hit unlucky as I went on that crazy day that hit almost 40 degrees in 2022.
You are really going to need a rest afterwards, so it may be prudent to do something gentle in the morning, and save the zoo for, say, 1pm that would allow you to have a rest afterwards. (Zoo is open 10 till 6 on a Sunday)
You can do evening ghost tours / daytime walking tours. There's one that includes the story of Greyfriars Bobby. Again, this might be a bit much in one day. Could be an option for the Monday before you leave.
A lot of Edinburgh includes walking (a bit like London, or any city for that matter) so be careful not to overdo it, or try to cram too much in. The castle is visible from the main streets, as is Arthur's seat so no need to actually trail around either. Perhaps an open top bus trip would be a good way to see some of the sights.
Best of luck and hope you all enjoy.
Oh, and one of my favourite things to do before I come home, is to pop to Harvey Nichols and treat myself to some bits from the food hall as we don't have one where I live.