I took a car from the Orphans' Fund Development Institution; is there usury (Riba) involved in this transaction?
                                If the Sharia's conditions were met, then there is no harm in this. And Allah The Exalted Knows Best.
                             
                        
                            
                                
                                Is it permissible for a praying person to make supplication in each Sajdah (a prostration) of obligatory prayer?
                                It is permissible for a praying person, whether praying individually, or in congregation, to make supplication during Sujood (prostration) in obligatory, or voluntary prayers. However, it is disliked for the Imam to do so since he is required to spare the prayer performers any sort of hardship, unless he is leading a certain group who don`t mind him extending the prayer.
                             
                        
                            
                                
                                Is it permissible for us to sever ties of kinship if our blood-relatives` gatherings/meetings involve acts of sin?
                                Observing kinship ties is obligatory, and paying your blood-relatives a visit causing their sinful acts to be hindered , then you should do so. However, if their sinful acts continue while you are at their gathering and they didn't respond positively, then observing kinship ties via telephone and the like will suffice in this case. And Allah Knows 
                             
                        
                            
                                
                                My husband told me that he concluded our marriage with a fake name that belongs to another person, because he was sentenced. Nowadays, he recieved an ID, passport and birth certificate with the his current name. What is the ruling on being married to him?
                                Praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.  As regards being married to the person mentioned in your question: The marriage is valid so long as he was the same person your guardian concluded the marriage with, even if he changed his name i.e. if your marriage contract was concluded with the same person, since what counts regarding marriage is the persons not names. And Allah Knows Best.