Help replacing unusual cast iron fitting

[jeffb53]

Had a leak from the upstairs bathroom in my 1927 house. Opened up the ceiling to find a cast iron fitting I've never seen before - looks like a 4" closet bend with two 1-1/2" inlets for the tub and sink. I'd like to replace this section with ABS but I'm not sure how to do it in the space available. Suggestions welcome.
Concerns:
Is it kosher to tie the sink and tub into the toilet trap arm?
Is the santee kosher?

Images:
CastIronUS_1 - stack comes up from bottom right and connects to a long 90°, a santee, and another long 90° that leads to the roof. Joists run left to right. Top to bottom members are just nailers.
CastIronUS_1 - closer view of the closet bend. plastic pipe is my recent repair, replacing tub trap and copper.

 

[James Henry]

You didn't say where the leak was.

 

[Sponsor]

 

[Plumber69]

Id get a plumber, expect over a 1000$ bill. You could cut the hub off and put a double wye in with a clamp and change toilet flange to. Joist is destroyed anyways

 

[Plumber69]

Like this

 

[jeffb53]

You didn't say where the leak was.

The 1-1/2" ABS in the picture was the leak repair. Actually, the brass extension tube coming from the tub drain into the trap was split, but I had to pull the trap out to get to it.
I'd like to replace ALL the cast iron shown while I have access. The vertical run below this was already replaced due to corrosion. I'm adding a bathroom downstairs and need to replace the cast iron in the basement anyway as well as tie into the cast iron vent in the attic.

 

[James Henry]

The 1-1/2" ABS in the picture was the leak repair. Actually, the brass extension tube coming from the tub drain into the trap was split, but I had to pull the trap out to get to it.
I'd like to replace ALL the cast iron shown while I have access. The vertical run below this was already replaced due to corrosion. I'm adding a bathroom downstairs and need to replace the cast iron in the basement anyway as well as tie into the cast iron vent in the attic.

Need a lot more information/sketches before anyone can help you.

 

[hj]

IT is a tapped closet bend and has been illegal for decades. I am not sure if they are even still being made.

 

[jeffb53]

IT is a tapped closet bend and has been illegal for decades. I am not sure if they are even still being made.

Thanks, hj.

 

[jeffb53]

Need a lot more information/sketches before anyone can help you.

Hope this helps. I can draw only a little better than I can sing.

 

[jeffb53]

Like this

Would this do the trick?