I have approximately ten animated objects on my timeline, but I only need to manipulate three of those at the same time because I want to re-scale them in time. How can I select the three objects I need, and only see their keyframes in the Dope sheet without messing with the others? When I try to select three, only one of the objects appears (last one selected).
You can turn on the Selected filter (mouse pointer icon) in the header of the dope sheet. Then the dope sheet will only display keyframes for the selected objects.