The hight temperature will be about 22C. It is pleasant traveling in Beijing and Tianjin at that time. You'd better prepare some long-sleeved T-shirts and confortable shoes for your parents, while you can wear summer clothes and sport shoes. It main be rainy sometime, remember to bring an umbrella with you.
Finally, Oct1~7 is the National Holidays when Beijing and Tianjian will be full of travellers. You will find every spot is crowded, be aware of it~

thanks for the information, its really helpful. i only reliase it was china national day after i paid for every thing. hope it would be a special and happy trip instead of the other way round.