Marrying a shia

Q: Is the Nikaah between a Sunni girl and a Shia boy halaal or not? The mother of boy is Sunni and the father is Shia. The same with their grand parents. They lived happily without interfering with each others maslak. They ask to do the Sunni nikaah and every thing according to our maslak. Please guide me with proper reference. The family of boy is not staunch. They don't do matam but they do disrespect the Sahaba ikram.

Associating with shias

Q: At our University we have Salaat al-Jumu'a in which 85% of the followers are of the Ahlus Sunnah wa al-Jama'a and 15% are of the Twelver Shi'a. The Shi'a stand in our Saf (rows) and pray with us. They do not bother us, nor do we bother them. But at the end of the day they are Shi'a, so should we the 85% tell them to leave and not pray with us? 

We have overheard their discussions in which many say wrong ahadith/rewayat, but their leader on our campus I have heard many a times scold the Shi'a and say that Hazrat Aisha is our Mother and is to be respected even if she made a mistake. Their leader keeps them in check. So are they Muslim? Can they pray with us?

Seeking forgivness

Q: How does one rectify one's shortcomings in Huququl Ibaad particularly when the concerned person has died. For example one had been disobedient or has hurt the feelings of his parents and the parents have died?

Reciting Sami Allahu liman Hamidah instead of Subhana Rabiyal A'laa

Q: When performing Salaah behind the Imaam, in the sujud after saying a few times "subhana rabbiyal alaa" somehow I was about to say "sami Allahu liman hamidah" but as soon as i said "sami Al" I realisized and cutt off and continued saying "subhana rabbiyal alaa". Now was my prayed invalidated since I cutt of at the half? Must I repeat it?