As you seem to be keen to get the best quality from your DVD I would suggest that you use FCPX and Share >DVD.
Although iDVD has better menus than FCPX, I believe you will get better quality from FCPX than iDVD.
iDVD is/was great for DVD quality in the days of DV tape,i.e. .dv
However iDVD seems to struggle with High Def material, going from 1920/1080 to 720/576 in UK (480 in US)
I experimented some months ago with FCPX Trial and found that FCPX>Share >DVD produced better quality than iDVD for HD material.
FCPX>Share>DVD automatically chooses the maximum quality bit rate up to about 2.5 hours per layer.
I would suggest you use 2 discs for your 2.2 hour video ( a good excuse for a break after first hour, they may need it?)
An hour on each disc will give better quality than 2 hours on one.
A DVD case can hold 2 discs." A keepsake package they can put on their book shelf."
You still could try dual layer if you wanted just the one disc.
If you do do 2 discs, then each half can be selected in the timeline for Share> DVD with In,Out points.