It is a different tax payer than you. 

To your question, for the Safe Harbor for Small Taxpayers (SHST), the property's Unadjusted Basis (i.e. excluding land, 100% bonus depreciation deduction, etc.) is probably around ~$300K.

The LLC is actually going to be the taxpayer and exchanger. 

The IRS is much more responsive to a borrow who is the tax payer than they are with anyone else. 

@Devon Daniels, if the tax auction was only 2-3 years ago, then redemption is done through the county probate judge or tax official (different counties, different departments) in charge of redemptions, not directly with the investor. if the investor is holding up the process because he/she refuses to sign off saying they are not owed anything for preservation improvements, then the taxpayer's remedy is to file a petition in Probate Court to redeem the property and establish the amount due to redeem. 

You may be able to deduct it under the de minimis safe harbor or safe harbor for small taxpayers, however under the BAR tests it would generally be considered a restoration as a major component of the plumbing subsystem is being replaced. 

Quietly exercise your taxpayer rights and call code enforcement. 

Would they still be responsible for the mortgage and tax payments once in my LLC?

When the gain from an installment sale of depreciable real property consists of both unrecaptured Section 1250 gain (25%-rate gain) and adjusted net capital gain, the taxpayer recognizes 25%-rate gain as payments are received before recognizing any adjusted net capital gainThis “front-loaded” allocation method is consistent with IRC § 1(h)(3)So depending on the amount of down payment, all the recapture might happen in the first year. 

Therefore if you take title as that LLC you are changing the tax payer from you which it is now.