Looking to add three bedrooms in the basement, one washroom (shower, toilet, sink), a small living area, and a small kitchen. Kitchen will just be an oven, a microwave and a sink + small counter top and one small cabinet on top of it maybe. This can be a very small kitchen.
A- This is a lowered back split on main floor (Family Room & Study room).
B- It has a 2nd floor on top of backsplit (~10 stairs to go up) on the main floor for bedrooms (called 2nd floor or higher backsplit?).
Because of the lowered backsplit, a great area in the basement is unusable (Utility and Storage area) due to lowered ceiling. Storage area is very low but Utility area is not so low but still can't walk up right.
I am looking for ideas on:
1- If I underpin the Utility or Storage area to give height, would it be a good decision given this is an almost 60 year old house. Any structural issues can appear? Is this usually done on a 60 year old house or not worth it / risk a lot?
2- If I don't underpin, how to use the Laundry room area (not built), and Recreation Room (built) to make three bedrooms for rent + kitchen and bathroom. Video here that shows unbuilt Laundry room area and built Recreation room: https://imgur.com/a/AKSln6k