technical modding issue

at this point i admit i cannot solve this on my own

how do i combine the build options of two factories into one factory without it acting like strider hub

i wish to use tweakunits or tweak defs if thats even possible

Please define "combine the build options of two factories into one factory"

Stick more buildoptions into a factory? Yeah that's doable, the engine has no limit as far as I know and it will happy let you stick every unit in the game into a single factory

The gui is a bit more complicated. The gui is only configured to show 11 units in the build menu. You could probably easily configure the gui to show more by editing the gui configs, but that's not something you can touch from tweakdefs/tweakunits, and you'll need to make a proper mod for it
As an example, tankium's more units mod expands the gui to fit in the extra units, but I'm sure you could easily configure factories to use tabs instead