I need to see contribution totals by families for a certain time period.

Go to Reports > New > Export Contributions (under the Financial section).

In the Options column, put in a file name and under "Summary Level" select Family and put in a date range.

In the Filters column, select Contributions, and in the "Total Contributions Amount" section, select the amount and date ranges you want to filter by.

Click "Go!" to run the report. The Excel document will automatically download to your computer, where you can open the spreadsheet to sort and manage it any way you want.