I am taking on the challenge of installing a toilet and sink on the second level of my house and wanted to confirm the best options for sewage lines. It's an older house and I'll be causing quite a bit of damage to existing walls/floors so want the best solution before I go ahead with this. I also believe the current plumbing is not correct so if I'm getting into it I figure I could put everything to right at the same time.

Attached is a sketch; the red pipes are the proposed new bathroom and black is the current drain system. From what I've read, there is a wet vent option which I think this is similar to but feel there's a reason I can't do this but I don't know why.

I'll leave it at that and look forward to your suggestions.

Thanks in advance,