Persuasion of any study is advisable for which you have intense passion. If you have that much interest for such certificates and would like to complete at least four by 2024, the same can be taken up from your end. I am missing one important aspect which you have not touched the subject with which are doing your Ph.D. Here I am not going to demotivate you from your goal but considering your subject in which you are doing a doctorate degree would help me to draw a better conclusion. If the subjects are Sanskrit, Philosophy, History like that, you can manage your time simultaneously for both your current Ph.D studies and proceeding for the certification course.
However, if the subject is of science stream such as one of these Mathematics, Physics, chemistry, Botany, Zoology etc, you would not have enough time for your involvement in other activities. If you undertake two missions simultaneously at least one or both will be affected thus not getting the desirable outcome.
Hence I would recommend to defer your certification course for which you have a mind at present and go ahead for your Ph. D course with your single minded devotion so that your thesis becomes impressive.