1. Make sure all images that need to be resized are in one folder (!)
2. Start Photoshop and import one of the images.
3. Hit ALT+F9 to bring up the Actions Panel.

Select the Action Tab and click the marked button, rename the action if you want and hit record.
4. Now every action you do is recorded and can be done by one click. Go to File -> Automate -> Fit Image ...
5. In this little window you enter the max height and the max width of your resized images. So images are resized in to a max height and a max width without beeing distorted.
6. Now go to File -> Save as ... and save the file somewhere, it'll be deleted later. When the JPEG Options pop up set it to 12 and hit okay.
Your Action Panel should now look like this.

7. Hit the square button to stop the recording.
8. Close your picture.
9. Go to File -> Automate -> Batch.
10. In this popup we need to do some stuff.

Okay top 2 settings (the ones under Play), just set it so that you Resizing action is set.
Source: Make sure folder is selected and hit Choose to select the folder with all the pictures in you want to resize.
Destination: Make it Folder and hit Choose and choose a folder where the resized pics should be saved at i'm sure you don't want to overwrite your dad's original shots.
Make sure to hit the "Over Action "Save as" Commands because otherwise it will ask you for the JPEG options when resizing ALL THE TIME FOR EVERY IMAGE.
Errors just make it log them and save the logfile somewhere it wont be needed but Photoshop complains allways and this only delays your work.
If it's all set hit Okay and sit back and wait until PS is done. All your resized images should now be in the folder you chose.