Kerry gave you some good advice.
I might approach it a bit differently.
Seeing as it's a series of home vids I would use DVD Shrink (free) to create 2 DVDs.
You can import your ISO into Shrink (from File choose 'Open disc image'), hit Re-author, then drag the titleset to the left pane. I would then use the 'Trim' function to find spot between 2 scenes, somewhere at about the half way mark ( 3+GB). This will be your end point. Note where it occurs.
Save this as DVD1. Reload the original ISO, go back to Trim again, now use the original end point as your Start point. Save this as DVD2.
The advantage to this is that you will now have DVDs that can can burned on regular (SL) blanks. Assuming you want to pass out copies to friends/relatives your chances of them playing on a wide range of players is greatly increased. Playback of DL discs can be a bit of a hit or miss proposition as can be the actual burning.
This guide is with an older version, but it should work. You will be choosing File-> Open Disc image to get started.
Get DVD Shrink here: