If you try to select several sheets in a spreadsheet, then right-click to copy, all but one come unselected. It's not possible to copy multiple sheets that way.
However, if you Ctrl Select or Shift Select the sheets by clicking on the sheet tabs, then choose Edit > Sheet > Move/Copy, then right-clicking doesn't disrupt the selection.
First, select the sheets you want to copy. Click on one, then hold down Shift and select the last one (select all sheet tabs between first and last) or hold down Ctrl and click on each specific sheet tab that you want. The sheet tabs will change color very very slightly, will be come slightly lighter, when they're selected.
Then choose Edit > Sheet > Move/Copy.
The option to Copy will already be marked and dimmed so you can't change it. Select the sheet after which you want the copies to appear.
Click OK and you'll see the copies.