I long arm for a charity group. I do not change my quilting style if it's a charity quilt, often doing custom quilting. The tops are made by folks with a wide range of skills. The group I work with has pre cut kits and offers basic instruction to new members. They also accept donated tops. They have a couple of experienced quilters who take a good look at the top before passing it on to the quilters, fixing seams that are too small and/or stuff that isn't going to 'quilt out'. Many points are cut off and/or seams don't match, but as long as the seams don't pull apart and the top lays sort of flat, it's good to go. The group also accepts fabric donations and so they can add a border to too small quilt tops.
If you quilt as a group, maybe you could buddy the folks up. Have a more experienced quilter sew while the less experienced person presses. Do they bring their own machines? If so, have an experienced group member help them figure out (and mark) a quarter inch seam.
As far as maintaining a 1/4" seam, well, just read this forum. There are lots of people who quilt a lot who can't do this!
I really think that having someone do the final pressing (and fixing if needed) is a good option. If you have one or two folks who's tops need to be totally re made every time, perhaps there's a different task you can assign them? Or how about holding a mandatory 1 hour class for people joining the group, including a demo of how you will tug on all seams of donated tops to make sure they don't come apart, so they should do that before turning them in.