Firstly copy one of the videos to your laptop and then right click on it and then click 'properties'.
That will tell you exactly what sort of file you have.
If it is .mp4 this software will play it:
http://www.downloadster.org/lp/vlc-player/356/?_u=bbd82effpnosaskamsbi67fbtqcat8acrcsphis94bckbbop4sv1-2c020f56f1fb316da8b974fb8a94ef9d
I would recommend that to anybody - it will play any music and video format and is perfectly safe.
You are right to save your precious videos in several places. A cheap and stable way is on dvd, if your laptop has a dvd burner as well as an external hard drive. I have no problem with saving video in the cloud as an extra copy, in fact it can be handy to be able to access the file from any pc or phone with internet connection at times. You can't have too many copies!
If the videos are in hd, copying them to your external hard drive won't affect them but if your laptop isn't hd it will only display in standard format.