I assume your sister just lived there and no rent was charged or paid.
You cost or basis in the house is the value on the date of death.
You will deduct your share of selling costs, and also add your share of any improvements to the house prior to selling it.
Your gain will be Long term capital gain (or loss).
If the tax you will owe is greater than $1,000 estimated taxes would be a good idea.
Below is the tax brackets and the capital gain rates for 2017.
http://www.schwab.com/public/schwab/nn/articles/Taxes-Whats-New