Don't worry about the load order of libraries.
You can't conrol the order in which they are registered with LibStub or CallbackHandler anyway.
What you can do is use your library's ToC fields effiecently. The
## OptionalDeps line, as you probably know, causes YOUR AddOn or library to check for the optional dependencies,
and load them before your AddOn or library.
Code:
## OptionalDeps: LibStub, CallbackHandler-1.0, LibOne-1.0, LibTwo-1.0
LibStub\LibStub.lua
CallbackHandler-1.0\CallbackHandler.lua
LibOne-1.0\LibOne-1.0.lua
LibTwo-1.0\LibTwo-1.0.lua
lib.xml -- or Core.lua, Main.lua, LibMyName.lua, etc