Good looking play place for sure, and I'm thinking hunting might also be in mind there.
For the other end of the bridge you might google "TAB treehouse attachment bolts" there are a couple of engineers who have gotten together and exchanged notes on bolt designs that worked well and did not work well. Accounting for how the tree is going to grow and so on. Pricey for sure but you are planning a very long bridge and might consider their advice. Start here: Treehouse Attachment Bolts (TABs) | Attached Limb Systems
Again, kudos on your good work.
For the other end of the bridge you might google "TAB treehouse attachment bolts" there are a couple of engineers who have gotten together and exchanged notes on bolt designs that worked well and did not work well. Accounting for how the tree is going to grow and so on. Pricey for sure but you are planning a very long bridge and might consider their advice. Start here: Treehouse Attachment Bolts (TABs) | Attached Limb Systems
Again, kudos on your good work.