your child stay crying to have your attention ,and to be more near to you than his siister and brother ,he might feel jealous,his character may be different than your other twins
TRY to look at the status deeply :he cries when you pamper him he stops >>then what he needs is your attention and your love and to specify him despite your other twin,then he maybe whenever he feels himslf in need to a hug or love or your attention ,he will cries even on non important causes ,he doesn't need a cause he will invent a cause to have what he needs ,he finds a method and he succeed ,he used it often then .
then if the problem is known now what can you make :
offer him more care ,many hugs ,many kisses,raise his self confidence ,raise his positive points infront of him and others let him know that you loves him too much and that he is a good boy ,don't blame him much if he make a mistake ,he might be sensitive more than others ,any single word will affect his feelings and children can't express they start cring on small things but the real cause is inside .
so give him your attention and pamper him frequently even before he ask for it through crying
if he cries ,don't pamper him ,don't give any attention to his cry ,just leave him ,after a while he will stop even if he don;t stop at first ,by time he will see his method is failing so he will not use it other time beside he will feel your warmness in other times .