Unfortunately, the current 'standard' grouping of Min languages is all wrong. Actually, Min languages can be grouped into only 3 distinct grouping i.e. Southern Min, Northern Min and Eastern Min.
1. Northern Min (Minbei, Minzhong, Shaojiang Min) - Both Shaojiang Min and Minzhong split off from Minbei around a few hundred years ago.They are all mutually unintelligible.
2. Eastern Min (Mindong, Manhua?, Manjiang?) - there are actually a few mutually unintelligible languages that split off from Mindong.
3. Southern Min (mentioned in thread below)
http://www.chinalanguage.com/forums/viewtopic.php?f=6&t=58902&sid=f62809c0fe89a197e2c1ad62d93df325
The historical establishment of Fuzhou city (Eastern Min) is quite different from the historical establishment of Quanzhou city (Southern Min) i.e. Quanzhou language didn't split off from Fuzhou language.
I somewhat (but not entirely) agree with the author of the link below. If we base languages on mutual intelligibility, there are at least a few thousand Chinese languages in China and not just 7 in the 'standard' classification.
https://robertlindsay.wordpress.com/2008/12/27/a-reworking-of-chinese-language-classification/