I would be tempted to tell Liebs that "farmer Christmas" is a figment of your mum and sister's imaginations, and he's not real but not to tell them that because they don't understand. And have a bit of a giggle about how silly they are. I really wish I had done that when everybody started telling my kids about Santa. Then they would have felt like they were in on a joke that everyone else was fooled by, whilst still enjoying the magic of Christmas without losing sight of why Christians celebrate at this time of year. Instead I have been bullied into Santa by everyone around me. DS1 almost doesn't believe now, and as soon as he asks me outright then I will tell him the truth.