Of course they are but it looks very indecent for a mature girl/woman to be pedalling on a bike. For young kids its ok though. Why not? But if a woman is wearing CORRECT islamic dress, impossible because her abaya would get caught in the wheel and she would fall
it depends if they are siblings or husband and wife or grandparents and grandchildren or uncles and nephews or niece, they are allowed to do so. for others, they are forbidden.