Are you in default on a loan?
I am, yes.
Then first you should make satisfactory repayment arrangements with the holder of the defaulted loan, if you don't do that first then you wouldn't be eligible.
And what do I have to do if the loans are with different loan servicers?
just submit a separate form to each of the servicers.
In my case, I taught at school that was included in the TCLI Directory only during my first year of teaching. Would the rest of my teaching years be counted towards the 5 years to qualify for the teacher loan forgiveness?
Yes, don't worry, the rest of your teaching years on that school will be counted as well.
How can I know if I qualify as a highly qualified teacher?
You must meet some basic requirements to qualify as a highly qualified teacher, with additional requirements depending of if you are a elementary or secondary school teacher and whether you're new to the teaching profession.
And how do I know if I'm teaching at a low-income school? I worked in an Indian reservation school.