Unfortunately you appear to have too much going on and the issues are beyond the scope of this forum.

I will, however, make some recommendations / comments:

• Since we are not able to see any documents (and certainly don't post anything since this is a public forum) we aren't able to determine exactly what is going on.
• I don't think you need an attorney at this point.  If you want to try and resolve this on your own, you can call or write the IRS to understand what has taken place with respect to your tax filings and lien.
• While I indicated you probably don't need an attorney, I would recommend you consult with a tax professional.  This individual can obtain a power of attorney from you and would be able to speak with the IRS on your behalf.  Yes, this will involve some out of pocket costs, but the cost of not resolving this may far exceed any tax professional fees.  Additionally, a tax professional has the ability to speak with a special group at the IRS to cut through some of the lower level red tape.
• Attached is a link to some general information on a federal lien that may provide some guidance and includes a phone number; https://www.irs.gov/businesses/small-businesses-self-employed/understanding-a-federal-tax-lien
• While you indicate the lien "was until 2015" just the fact that this is on your credit is reason enough to follow up on this to get this removed.  Unfortunately this issue will take some time to resolve.  The IRS is understaffed and moves at a sloth pace.