I think you have three cascading drop downs which have a hierarchy and connections between the tables and fields to enable you to filter dynamically.
There isn’t an easy front end solution (in my opinion) to allow users to add a new option without ensuring it has the other associated records to allow the cascade to work.
If I was building it would be an admin function
It possibly requires a user with a higher understanding of the relationships for the cascading drop downs to set them up with a new option correctly.
No simple answer to this as you have a fairly complex setup that is dependant on other values in different objects.
Letting end users add options to objects is often fraught with challenges around data integrity.
For example, a user may add: England, Britain, UK or United Kingdom and they are all pretty much the same county but you’ll have four values.
That doesn’t include those users who don’t check to see if an option is already in the list so they add it again, or a slightly different spelling, to get around the “unique” option.