Your description suggests a time frame of 6 months or less. However you should ask your father’s doctor as he/she is in the best position to make an “educated guess”.
Your second question is harder. Your mother's denial may be a reasonable way for her to cope with what is happening. You have no obligation to "make her deal with it." You should also ask yourself if your desire to "make her deal with her denial" is to make this situation easier for you.