With the price of plastic pipe being what it is, . . . I'd run all separate lines out from each of those bad thingys.
The toilet needs to be on a 3 inch line, . . . the others can be 1 1/2, . . . cheap at twice the price.
You want at least 1/16 of an inch per foot drop from entrance to exit, . . . not over 1/8 of an inch per foot, especially on the toilet. Too little drop and it don't go no where, . . . too great a drop, . . . and the water goes, but leaves the solids, . . . which plugs up the system. THAT is the first thing I would look at, . . . solid stuff laying in the pipe.
And if your wife has a garbage disposal, . . . take it out, . . . throw it away, . . . buy her a scrap bucket at Loews, . . . blue 5 gal buckets are $2.99 with lid, . . . dump out back for the possums every day or so.
I don't know a bunch about plumbing, . . . but I did try to put a 1 1/2 inch thru the roof vent when we started building our house, . . . inspector made me change it to a 3", said I would have all kinds of trouble if I didn't change it.
Have not had any problems at all with our system.
May God bless,