When you start a new movie with them the timeline will be automatically set to their resolution and frame rate.
You can easily match the resoultion and frame rate by using the Same as Timeline checkbox in the Export.
If some of these old video are using old codecs, do you really want to use the same older, less efficient video codec? Studio can detect mpeg-2 SD and use that, but you will just end up with a larger file than you need.
It may be that you don't want to re-encode the video - Direct Stream copy - so that the video doesn't get any further degradation, but Studio can only do this with mp4.h,264 anyway.