will there be less sequence during 24-26 Dec for both metro and train to airport?
Frequency of Paris Metro & RER trains on Christmas day will be the same as a Sunday or other holiday days.
You can find RER B train schedules here: https://parisbytrain.com/paris-rer-b-schedule-stations-interchanges/
The current schedule files are a few years old, which will be updated after the summer construction works are completed August 20, but even the old schedules will be very similar to current times. Note that the weekend & holiday RER B train schedule towards CDG and RER B train schedule to Paris center are located at the ends of the PDF file.