Macerator pump for a toilet & sink using existing shower pipe

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Hello. I am planning to build a small half bath in my garage, next to a washing machine, using old showers plumbing. There was a stand-alone shower in the garage which has been removed. Unfortunately the pipes are only 1.5" on that side of the house since there's no bathroom and the house is pretty old, so the only way seems to be a macerator pump. The washing machine drains into a stand pipe, there's also a sink tied into the stand pipe, then the stand pipe ties into a vent pipe. I am not sure where does the showers drain go, but there is a visible bulge in the slab which ends in the middle of the garage. I assume that both, vent pipe and shower drain are tied into the same line that goes from a kitchen sink, but I might be wrong. The walls concrete block and there's a concrete slab which makes it more difficult. I am located in central Florida.

Would the macerator pump require a vent?
Can I use a AAV or vent it through the wall?
If not, can I tie the macerator vent into the washers vent?
Can I extend the shower drain and use a 90 to put it along the wall for the macerator?
What is the easiest way of plumbing it so that it works fine?

I would really appreciate if someone could help me with the plumbing plan.

Here is how it looks like:
And a little sketch to give you a better understanding (The blue pipe and blue circles are questionable since it's burried in concrete):
And this is what I am planning:
Hey, wait a minute.

This is awkward, but...

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