"can I deduct mortgage"

No.

"and property tax on Schedule C"

Possibly.

The mortgage that is against the amount borrowed (the "principal") is the cost of the land. There is no Deduction for this, because the value isn't a write off. It's an investment. It's right there = in the Land. They now own land. This is called Basis. If this is new to you, you will want to read up on this concept.