Looking at buying property that has liens but will use owner finance

[Rick Mroch]

I'm looking at buying a property from a couple that would like to move out. This will be an investment property long term for me.  It is a split level unit that has basically an upstairs apartment and downstairs apt. Right now they live in the upstairs and rent the downstairs. I have discussed with them doing a owner finance and me purchasing from them. I would take possession of property and pay them directly.  Once i take possession I would rent the upper unit or move in /rehab it then rent. The property has a lien on it and I need some help putting together a deal that would be as iron clad as possible. Any help, suggestions or knowledge transfer from folks experienced in this would be greatly appreciated.