Can i bring 1 iphone 7plus & 1 iphone 6plus. 1 powerbank 20000mah (74wh) & 1 powerbank 10000mah

Yes, you can take two phones but you are suggested to unwrap the outer package. However, you can take at most 2 power banks but the total capacity cannot be over 20000mah, so may be you can only take one power bank 20000mah or two power banks 10000mah.