What are an heirs rights regarding the sale of real property that they inherited?

First of all, since your mother died without a Will, her heirs would be a surviving spouse, if any, and her children. Since you don't mention a father (or stepfather) I will assume that there is none. Accordingly, you and your 2 siblings would share equally in your mother's estate. Now what needs to be done is for a probate to be opened up in the local probate court in the area of her residence. For certain small estates, there is an expedited process for distributing an estate (so a formal probate need not be done).

At such point at the propety is titled in you and your siblings names, you can then take action on just what to do with the property. You can file a "partition". This is a legal remedy employed when the co-owners of real estate cannot agree as to ownership matters. Basically, it means the division of property among co-owners. If a property can be physically divided the court will so instruct. However, where division would be impracticable, as in the case with a single family house, the court will order a "sale in lieu of partition". Accordingly, there would be a sale of the property and an equitable division of the proceeds among the co-owners. Before such a sale would be ordered, the court would permit one co-owner to purchase the interest of the remaining co-owner at fair market value.

Since this can all get a bit complicated (and expensive), try to work things out with your sister. If that's not possible, then consulting with real estate attorney at this point would be in order.