Cycling into Istanbul

Hi. I am really hoping someone can help me with this question or pass it on to someone who might. I have friends who have been cycling from Sweden, down through Europe and they want to finish in Istanbul. I have no idea how they could manage the traffic and end up where I live (Emirgan). Just appears too daunting to me! Could they cycle to a train station on the outskirts of Istanbul? Are bikes even allowed on trains here? What would be the best route into and through Istanbul to Emirgan? Is it even possible? I would be so grateful for feedback of any sort. Many thanks Kaylee