4 x 6 =36 square feet, enough for about 9 full size hens, are you sure your measurements are right? If you have 13 nine month birds doing fine in there, that is great, but that is pretty tight to add other birds.
Thing is about the bantam and large fowl - even though they are BF now, it is not...
I like option 3 too! However, some people do successfully run LF with Bantams. Have you added chicks before to the flock? Some flocks take to it easily and others become predators.
A lot depends on your set up. If you have space, a lot of hideouts set up in both runs. I think what I would do is...