Unilateral notice or Lien

Does anyone have experience putting a UN1 Unilateral notice against a property. Funds having been used to invest in a new property that should not have been invested in said property - the funds were a loan that was due to be repaid. Unfortunately there is not a loan document. Funds came from the sale of property A , the same solicitor was used for the sale of A and the purchase of property B - the owners of property A and B were not the same parties. We have been advised that Independant legal advice should have been given or a conflict of interest raised as this would have prompted a loan document to be put in place - not hard to guess that this involves family. Legal advice appreciated, there is a long history of messages and emails clarifying ownership percentages and a forensic accountant has come up with accounts for Property sales and profit and what should have gone to who. two family members are owed money by two other family members. Any advice appreciated where would people start with this mess? I am poised to get a Second Accountant to do second rendition.