If you have Turbotax installed on your computer from a CD or download, you can prepare as many returns as you like for family, as large as you do not charge a fee. Each return is a separate document, like having more than one spreadsheet file. However, you can only e-file up to 5 returns. More than that, and you will have to print and mail them. This is an IRS limit, not a Turbotax limit.
You should not try to install more than one copy of the Turbotax program -- strange things have been known to happen. And you don't need to.