Most commercial DVD’s are DL, so squeezing two DL movies onto a dvd with special features will result in a massive quality loss.
Squeezing a DL movie onto a SL disc with the Special features/menu’s usually means sacrificing the quality of the special features to maximise the available space for the movie.
My first guess would be that the quality loss (video) for the two movies with special features would practically make them unwatchable, unless you were technically blind.
Why not just compress both DVD’s onto SL media?
Two SL media is cheaper & provides a slightly larger capacity (and hence slightly increased quality) than a single DL media.