A few notes on formula feeding with older squirrels:
The same squirrel may have not interest in formula one day then eat voraciously the next. A squirrel may even skip a couple days then resume.
I just overwintered two sisters (released now) and they were still taking formula once a day when they were 22 weeks old. While this is far longer than I have seen in other squirrels, if your guys are undernourished (as seems likely) they may well be quite happy taking formula.
I had an NR Ziggy (quadriplegic) and he got FV 20/50 his entire life. My point being that this is a great way to assure nourishment at any age.
You may want to experiment with formula feeding through the wire. If you pick a spot where they can stand on something with the syringe at head height, this often works quite well. While with younger squirrels holding them to feed is preferred, past a certain age they are not likely to want you holding them anyways. I usually transition to feeding formula through the wire at some point. I have only had two squirrels max, and feeding through the wire ends up involving quite a bit of switching.
With eight it will be be interesting no matter how you do it - good luck and post pictures!