I would let them know that their Christmas and b-day gifts will be donated to worthy causes in the interests of spreading the wealth around. You can be very pious and serious when you send them a card telling them just who received whatever instead of them. Avoid emotional screeds and simply tell them this is the consequences of socialism.
My one adult child is a Libertarian/3rd party voter who has told us he would vote donk if there wasn’t an L on the ticket. I know how you feel. We are very upfront when he starts in on politics. We have confronted him with facts and get facile retorts in return. My DIL thinks our arguing is rude, but so what? They need to think beyond their ideologies and consider the future of the country. We have kept their gifts at a low average amount and tended towards small, highly practical gifts instead. Long underwear is good for those in Northern climates. Not sure what you could do for those in warmer climes. Maybe a good book on conservative values?
I actually hven’t sent them a dime or gift in some time. I am so fed up with their attitudes. But then again my 88 year old mother voted for BO, this from a Catholic woman, because McCain is a war monger!