QUESTION Can horizontal drains combine through a wye in the horizontal position laying flat on its side and not upright at all, Or Can't They?  Then see my sketch: Am I doing this right? - Merry

IPC TABLE 706.3 "fittings for change of direction" says wye is okay for horizontal to horizontal.

Are my proposed wyes okay?  How about overall?  I don't want to go down too low with the drains or relocate much stuff. 

[![This is just a sketch - Am I doing this right?][1]][1]
BACKGROUND:  This is just a draft but in the interest of limited headroom and headache I want the plumbing improvements to not descend too low into the door/passageway below, and I dont want to change the lower level toilet system, an older wall mount model, except just to vent it, without moving the bracket, and to drain the upper level bathroom through a separate pipe and vent it.  And most obviously there is improper use of a sanitary tee and that needs to be rectified.

  [1]: https://i.sstatic.net/81jXq.jpg