Is it permissible for someone to make a supplication to Allah to marry an already married, or an engaged woman?
                                No, it isn`t, and the person who does so is sinful before Allah, The Almighty.
                             
                        
                            
                                
                                Is it permissible to have sexual intercourse with pregnant wife? 
                                All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
There is no sin in having sex with one`s pregnant wife as long as there is no medical condition preventing her from that. And Allah The Almighty Knows Best.
                             
                        
                            
                                
                                I am a disabled woman who has vaginal discharges and can`t control her urine. Therefore, I combine prayers. Is that permissible?
                                All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all his family and companions.
According to the Hanbali doctrine, it is permissible for the sick to combine prayers. In your case (Asker), it is better that you delay the noon prayer until a few minutes before the afternoon prayer in order to minimize the time span between the two and perform each alone. In addition, you can do the same with sunset and evening prayers. Finally, we ask Allah to bless you with recovery. And Allah Knows Best.
                             
                        
                            
                                
                                My brother is settling a debt on my behalf and in return he takes 30% interest as an additional amount of the whole sum. Is this lawful or not?
                                This additional amount is considered prohibited interest (Riba) according to Islamic law, and it is not permissible to take it. And Allah Knows Best.