My advice, worth exactly what you’re paying for it:
First, decide whether you think it’s more likely that…
...they really do understand your state, and their experience of Christmas will be genuinely sullied by sharing it with a child who doesn’t worship Jesus, or
...they don’t really understand your state, but they are sincere that their experience of Christmas would be sullied by sharing it with a child who has whatever attributes they are inferring you have, or
...they aren’t at all sincere, and are threatening to withhold Christmas from you as a way of pressuring you into recanting your atheism and asserting the beliefs they’d prefer you assert.
(Other things are possible, as are combinations. Those seem the likeliest options in the absence of details about your family, though.)
Given #1, I’d advise finding others to celebrate Christmas with, and letting your parents know that if they ever change their minds and welcome you into their Christmas celebration you’d be happy to share it with them. Given #2, I’d advise looking for new ways to communicate your actual beliefs to them. Given #3, I’d advise letting them know that’s what you think they’re doing and finding others to celebrate Christmas with.
My advice, worth exactly what you’re paying for it:
First, decide whether you think it’s more likely that…
...they really do understand your state, and their experience of Christmas will be genuinely sullied by sharing it with a child who doesn’t worship Jesus, or
...they don’t really understand your state, but they are sincere that their experience of Christmas would be sullied by sharing it with a child who has whatever attributes they are inferring you have, or
...they aren’t at all sincere, and are threatening to withhold Christmas from you as a way of pressuring you into recanting your atheism and asserting the beliefs they’d prefer you assert.
(Other things are possible, as are combinations. Those seem the likeliest options in the absence of details about your family, though.)
Given #1, I’d advise finding others to celebrate Christmas with, and letting your parents know that if they ever change their minds and welcome you into their Christmas celebration you’d be happy to share it with them.
Given #2, I’d advise looking for new ways to communicate your actual beliefs to them.
Given #3, I’d advise letting them know that’s what you think they’re doing and finding others to celebrate Christmas with.