No. The "suus" should not be there. Not only is it placed first and thus with great emphasis (...et filius suus Marcus wouldn't have been as inappropriate) but "filius", son, is in such close relation and nominative subject connected by conjunction "et", that the "suus", his (own) is understood. i.e. it does not need to be expressed.
It's like "mother and I went to town" - you don't really need to clarify that it was your mother, for you are so closely related. Of whom else is mother going to be? The same with filius.
However if you were to say Sextus legatus et filius eius, with "eius" meaning his or of him, it would mean Sextus the lieutenant and (some other guy's) son, not "his own" which is suus, a , um - the possessive reflexive.
This is quite important - Latin is very different in that certain things are understood (not expressed) because they may be understood without being expressed. Indeed, if you are ever marked on a prose composition, less idiomatic unnecessary "suus" 's and many other understood elements which you shall encounter depending on the situation of course, are very much frowned upon - as clumsy latin.
Good luck with your D'Ooge course.