Trouble shooting poor hatch rate for a neighbor

Twice my neighbors (down the road) have had me take the eggs their broodies were setting. Both cases were a little extraordinary I realize, but I don't think the eggs should be having this much trouble.
The first was a mama who hatched 2 chicks and left the nest. 48 hours later I got a call and rushed them to the incubator to try and help them out. Out of 15 eggs, 1 hatched 2 weeks later and is now thriving. Most started to hatch, pipped, zipped, etc, then just gave up before freeing themselves of the shell. I chalked that up to having been sporadically incubated for 48 hours during what should have been 'lock down'.

This last time they caught a hen with 25 eggs. At least 15 of the eggs were between 8 and 15 days along. The other 10 were less than 4 days along. It's been touch-and-go for the last 2 weeks in my little LG. 1 hatched 7 ago. Strong and thriving. Another hatched 3 days ago- it was upside-down in the shell. It zipped about an inch and couldn't seem to move from the position it was in, so I 'unzipped' the shell and waited a day. No progress. So I worked it a little more and waited again. This time he got out. Meanwhile another chick had spent 3 days wearily zipping and finally hatched 2 days ago. He's small. They're thriving, but neither properly absorbed the yolk (there's like a big pink lump where there should be a scab). The upside-down chick's legs are very weak and turned inward a bit. Many other chicks pipped and just died with their beak out. About 10 of the eggs died earlier in development. That broody hen was allowed to keep 2 eggs from the lot. 1 hatched (the other turned out infertile) and just died within 3 days for no apparent reason. She's now raising the 7 day old chick and so far so good. I've kept the other two because they're so weak.

My point being, it doesn't seem like these chicks should be having this hard of a time. I hatched about 100 of my own eggs this year, and even with scary temp spikes (or dips!), rough handling, improper humidity (this was my first year, still learning), etc., I'd get 13 out of 15 eggs to hatch pretty consistently. And though I've had accidents with chicks, I haven't had any illness-related or mystery deaths form either incubator chicks or broody chicks. The only deformity was one chick with a cross-beak (whose mother has a minor cross beak). So I'm taken aback to see so many issues here!

My neighbors are feeling a little crushed. I think this is their first year with chickens(?) and they're learning. Coyotes have been ravaging their flock and they're hoping for some 2nd generation birds. What can I recommend? It seems like maybe a nutrition issue for the eggs to be dying consistently around day 15-17 and right at hatch, not to mention unhealthy chicks and failure to thrive. Their birds roam 13 acres, shared with horses, ducks, cats, dogs, and sheep. They're fed Purina pellets if I recall correctly. I think they raised their 1st gen chicks on medicated feed. The late chick that the broody hatched was eating medicated crumbles. I know there are a lot of differing opinions and I'm not looking to argue, but I already recommended they bin the meds. I've seen friends and neighbors loose chicks like mad (even from the same clutch) and the only difference in our brooding has been the meds. I'd like to recommend getting away from Purina, too, and opt for a local milled feed. Thoughts on what I can do to help them?