Unfortunately, it is not possible to add your son to the application if he is independent. By MRVP legal note, you can add a child if at the time of application he is over 18 years of age, not married, and who proves that at the time of application he is not economically active and is principally dependent on the main applicant.
Who can qualify as dependent for the Malta Residence and Visa Program?
Recently I heard that Malta has removed the age limit on adult dependents of MRVP applications. My wife and I are very interested in applying for this program. My son is 29 years old, unmarried and financially independent. Could he qualify as our dependent in the MRVP application?
A child of the main applicant who is over the age of 18, he or she shall be classified as a dependent if he/she is not married at the time of application, can prove not being economically active and is principally dependent on the main applicant. Therefore, if your son is currently employed or earning an income with which he can be deemed to be financially independent, he shall not qualify as a dependent in terms of the law regulating the Malta Visa and Residence Program.
Your understanding of the MRVP program is correct. However, it is important to note that for your son to be considered a dependent under your application, he has to be financially dependent on you. Otherwise, he would have to apply under a separate application.