We've had numerous inspections and site visits with contractors and she is quite aware that when we take possession, that the remodeling will begin in the in law and a large out building but not in the unit she's in until she moves.  

How do you market a property with possession being unknown?

Notice to quit.(1) A tenancy may be terminated by notice in writing, served not less than the respective period fixed before the end of the applicable tenancy, as follows:(a) A tenancy for one year or longer, three months;(b) A tenancy of six months or longer but less than a year, one month;(c) A tenancy of one month or longer but less than six months, ten days;(d) A tenancy of one week or longer but less than one month, or a tenancy at will, three days;(e) A tenancy for less than one week, one day.(2) Such notice shall describe the property and the particular time when the tenancy will terminate and shall be signed by the landlord or tenant, the party giving such notice or his agent or attorney.(3) Any person in possession of real property with the assent of the owner is presumed to be a tenant at will until the contrary is shown.(4) No notice to quit shall be necessary from or to a tenant whose term is, by agreement, to end at a time certain. (5) Except as otherwise provided in section 38-33-112, C.R.S., the provisions of subsections (1) and (4) of this section shall not apply to the termination of a residential tenancy during the ninety-day period provided for in said section.

The tax certificate for the first 3-4 years has been purchased by an investor, and after talking to the county it seems like this year it will likely be possessed and put to auction.I've managed to reach the owner through snail mail, who is an elderly couple who called me back and left a VM basically sounding like they don't want anything to do with the lot. 

When we close and take possession we will be requiring they sign a one year lease if they would like to stay (they've lived there for 12 years so I am not too worried that they'll put up a huge fuss).

My lease has a clause that says if they do not take possession of the premise in seven days (a.k.a move in inspection with me) then they loose deposit.

Just be glad you got possession back without a fight. 

I have a ton of furniture and possessions and I'm quite dismayed about what to do.

I will gain possession 4/10/19 and I plan to have it rented by June 1st.

If she moves out of state, then you can take possession of the apartment through abandonment.