Double Stroller question

MJ

My sister-in-law bought us the Baby Jogger City Mini GT double jogging stroller for our twins. Do I need to register for a tandem stroller also? I’m not sure if/how car seats go in a jogging stroller. SIL lives 6 hours away so I won’t have it to look at until my shower. FTM obviously🤷🏼‍♀️🤦🏼‍♀️