[Ayesh]

You can easily fix the low quality PR issue with a CI setup.

Setup a Travis job to fail often (build, lint, test, coverage, etc), so you pressure them PR author to complete it. This will make the entry barrier massive, but helps you focus your attention.

In addition, take an hour setting up issue and PR templates and guidelines in GitHub. A good readme with an FAQ section helps too.

See Symfony/Symfony for a good example.