Public health department may consider the above risk and deem that house uninhabitable. cannnot get insurance, can not rent....
I suggest you talk to city and ask where sewage connection is and ask them to recommmend contractors to estimate the cost of replacing the septic tank or connecting to city sewer.
There may be need to cut down some trees and to remove their roots for tank replacement. $$
https://www.epa.gov/septic/resolving-septic-system-malfunctions