As far as the SSDI goes if you flip the IRS thing (SSA-1099) over there is a worksheet to help you see if it is taxable. Actually I think it will help you with your entire question. Basically you take your SSDI amount, divide it in 2, add any taxable income, add any tax-exempt interest and total. Then there are options listed and you figure out what you fit into.

I seem to remember that employer related disability depends on whether you paid for the plan or the employer did. But that was a long time ago and I don't remember the details beyond that.

Good luck. I know how hard it can be. My federal student loans were forgiven my first year on disability and trying to figure out taxes that year was ridiculous.