Is a son considered disobedient to his mother if she stops speaking to him because he refused to celebrate a birthday and did not kiss his uncle's wife? And has he committed a sin if he is forced to go to a birthday party while he dislikes it? And is there any blame upon him if he accepts money from them on his birthday?

You are right in your pursuit of righteousness and your eagerness to please Allah. We advise you to supplicate for your family, asking Allah to guide them. Remain steadfast in avoiding participation with your family in Christmas celebrations and kissing your maternal uncle's wife, for people's anger is normal on this path. Work towards what pleases Allah, even if people become displeased, for the ultimate outcome is for the righteous. It is not permissible for you to be present in a place of wrongdoing unless with the intention of denouncing it. If it is not possible to denounce it except by the heart, then denouncing it by the heart requires leaving the place of wrongdoing. It is not legislated to give gifts specifically for Christmas occasions, and whoever does not fear harm by not accepting them, it is better for them not to accept them. If your mother becomes angry with you because of your adherence to the truth, that is not an act of disobedience on your part towards her. We advise you to be gentle with her and to appease her.