I read it all so might as well answer:
1. Some stuff comes with experience, painful experience at times. I think you're learning something new here, so see it as opportunity to improve.
2. INFJs do have a problem with setting boundaries and being hard on people. I had hard time grading down people turning in their homework late. What I've done in past is devise rules and pass them to everyone in written form. If somebody broke rules, wasn't my fault, I just enforced them and marked down exact amount that was specified.
3. As a result of being too permissive yes I have in past completed work for others.
4. Sounds like people you are working with suck. What are they doing there? Getting paid? Have they zero vision?
5. I think they need some stronger incentives to un-suck. Is there any sort of pressure you can apply on the slackers? There is a saying in my native country that goes "laziness was born before human kind" and it is true.
I have no idea what you posted Curious but Vel mentions slackers and I have worked with a slacker. We were job sharing so I would come in one half of the week and she the other half. I used to find that I ended up doing all the work! And my brother who worked in the same office (full-time) could see the difference between the both of us and said that she just sits there messing with her phone and singing most of the time, where as I would be getting things done. Sorting out problems, streamlining procedures!
Now that I've left my job my brother says that she has improved a lot. I think she realises that she doesn't have me to fall back on and that she actually has to do what she's paid to do!