Call and pay an architect, structural engineer or licensed carpenter. That fact that you would ask such a complicated, open-ended, liability laden and potentially hazardous question online indicates you are well on the road to disaster.
Your conditions need to be visually inspected and assessed by a qualified person. Do not believe all the HGTV hype a DIY cannot do everything.

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Accurate Inspections & Consulting, Inc.
773/844-4AIC
Markus Keller