We have no inside information on Christmas moods at the home of these Australian siblings and party colleagues but we can't imagine the conversation over the prawns and mango stays festive and airy when the topic of same-sex marriage comes up.
Their views are as different as chalk and cheese.
Tony Abbott, former Prime Minister of Australia, Liberal MP for Warringah, tried on Wednesday to rally the vote against same-sex marriage in a forthcoming postal vote. He's pushing attempts to get a public vote on the matter instead of a parliamentary one. Critics call it a delaying tactic.
His sister, Christine Forster, Liberal councillor in Sydney, has been engaged to her same-sex partner Virginia Edwards for nearly four years and wants gay marriage across the country.
So when Mr Abbott told reporters why a no vote was important, Ms Forster tweeted her take on the matter, line by line:
Mr Abbott: "If you don't like same-sex marriage: vote no."
Mr Abbott: "If you are worried about freedom of speech and freedom of religion, vote no."
Mr Abbott: "If you don't like political correctness, vote no, because this is the best way to stop it in its tracks."
Ms Forster has sparred with her brother in public before. In 2015 while he was the prime minister, she appeared in a rap video calling for tampon taxes to be cut.
Tampons are still classed as luxury items and therefore subject to a 10% tax in Australia. Proposals to cut the tax went to the Senate but were voted down.
A Buzzfeed reporter asked Ms Forster if the tweets were meant for her brother. She said: "Of course they were".