Not all of the names you mentioned in your question had really claimed Imamate,but it is a fact that some of the children or grandchildren of curtain imams did wrongly claim Imamate.The reasons behind that were mostly political and for gaining worldly benefits. All those who wrongly claimed Imamate had failed,despite the political and financial support from the rulers and governments of their times who were always interested and keen to create dispute between the followers of Ahlulbayt. Being a son or a grandson of the Infallible Imam does not mean that he is also an Infallible,we read in Quran how one of the sons of prophet Adam [AS] did kill his own brother. Al-madeena [5]. We also read in Quran about the son of prophet Noah who disobeyed Allah and his father.Hud[45]. It is worth mentioning that most of those sons of grand sons who did wrong have repented their mistakes.

wasalam.