I think the point around Farage is the following timeline:
He claimed that he was buying a house in his constituency some time ago - told a reporter that it was in the process of going through.
When the purchase was confirmed people looked into it and said "ah ha, the regular rate of stamp duty has been paid! He's fiddling his taxes!"
Farage responds saying the house was in fact bought by his partner with money from her family and therefore nothing to do with him.
BBC investigates and finds out her family aren't "wealthy" as Farage claimed and unlikely to have £850k lying around in cash to gift to her.
So the questions are:
Did he give her the money to buy the property?
If so why did he lie about it?
Did he give her the money in order to dodge the stamp duty payment?
If the sale is nothing to do with him why has he instructed tax specialists to look into things?