Is the failure to send money to a well-off father considered disobedience, given the need for it to spend on one's children?

There is no blame upon you, nor would you be undutiful to your father if you do not send him money, as long as he is well-off, and you only possess what suffices for your family's expenses. Providing for a poor father is incumbent upon his well-off son, and although a father may take from his son's wealth, that is conditional upon certain stipulations. Strive to please him with what is available to you, and treat him kindly as part of fulfilling the duty of dutifulness to parents.