I would expect this to go to court. His case clearly is that you hit him and yours is vice versa. He can ask his two witnesses to give evidence (there are no rules about them not being valid because they lack independence) but the fact that they are known to him may make the Judge give them less weight. Your insurance company should send a barrister to represent you, who will be able to cross examine those witnesses and hopefully, in probing the detail will be able to show them to be not consistent or credible. You should make sure your insurance company gets witness statements off your witnesses. Also make sure that your statement contains as much detail as you are able to give. Also, make sure it is CORRECT before you sign it (I know that sounds obvious but so many people sign the statement and then decide it is incorrect).