1) I wanted to ask what is the Shia argument for when the Sunnis says that uthman married two of the daughters prophet ruqyah and in kulthum on the basis we all agree they were the daughter of the prophet and Khadijah.
2) What is the argument when they say according to Arabic grammar in the Quran the feet are to be washed and not wiped

1- There is big debate about whether the three daughters where the daughters of Prophet, or the daughters of Khadeeja from previous husbands.
However, even if they were his daughters, there is no problem in marrying them to any Muslim, as there is only one Ali Bin Abi Talib, and the other daughters for sure were not of the same category and level of Fatima AS. This something agreed by all Muslims.
2- According to Quran and Arabic accurate grammer, feet are wiped, not washed.