If you do not have a way to get anything bigger than a single bed into the basement by any other means than the basement stairs, then save you and them some time and bring them right to the funeral home!
How are they going to get out in a fire?
Isn't there a regular door in the basement?
Is there going to be atleast 5.7 square feet of egress in every bedroom going directly to the outside world?
Have you gone to your local Building Inspector to find out what is required to create this dwelling unit in your basement? (I'm thinking not!)
Smoke detectors, egress rquirements and such.
Do you have a furnace and hot water heater down there? How about a carbon monoxide detector?
If you finish this area off, do you have enough "make up air" for the furnace and water heater? Or do you think they will just burn the air the grand kids are supposed to be getting?
Sure, I can tell you how to level the house and yes, there will probably be some damage upstairs. "For every action there is an equll and opposit reaction".
Please do you family a favor and maybe save their lives, get the permits and the inspections that go with them!
A side note* your insurance company is going to look to see if this work was done legally if something goes tragicaly wrong!
I wish you and your family well and I hope I have convinced you that you may be doing more of a dis-service to your daughter than a favor unless it can be done right!