The village might experience a huge boost in morale. Naruto killing Pain would be seen as a major victory, and the villagers would feel safer. They would look at Naruto as an even greater hero, which could lead to more trust and unity within the village.
In fanfiction, the idea of Naruto attacking Kushina is very uncharacteristic as they are mother - son. It could be a very dark or alternate universe scenario. Maybe in a plot where Naruto is mind - controlled or in a completely warped reality where family bonds are reversed.
In many fanfictions, Naruto might use new jutsus or a deeper understanding of his own power. Maybe he taps into a more powerful form of the Nine - Tails' chakra and combines it with his Sage Mode in a unique way to overpower Pain.
Naruto would likely be deeply hurt, not just physically but also emotionally. He has always idolized his mother, so an attack from her would be a huge blow to his psyche. His trust in family and those close to him could be severely damaged.
In some fanfictions, Naruto's pain might manifest through his actions. For example, he could become withdrawn and isolate himself from his friends. This is because Naruto has always been a social person, so any deviation from his normal behavior could be a sign of his internal pain.
One possible cause could be his sense of failure. Naruto always wants to protect his friends and village, so if he fails in a mission or is unable to save someone, it can cause him great pain.
Definitely Sasuke. Their bond is such that Sasuke would not stand by and let Naruto destroy Konoha. He has his own reasons to protect the village now. Shikamaru is also a likely candidate. He's intelligent and would quickly figure out that Naruto's actions are wrong. He would use his strategic mind to try and stop Naruto. And Hinata, who loves Naruto deeply, would oppose him in the hopes of bringing him back to his senses.
He may also choose to defend himself without really fighting back. Naruto values Sakura as a friend and teammate, so he would be reluctant to harm her. He might just try to dodge her attacks and keep talking to her, hoping to snap her out of it.
Perhaps there's a time - travel element involved. Naruto from the future, who has been through some horrible experiences, travels back in time and, in a state of confusion or rage, attacks Kushina. Or it could be that a powerful villain has the ability to manipulate Naruto's emotions and uses that power to make him turn on his mother. This would create a very complex and dark plotline that challenges the normal Naruto narrative.
In this fanfiction scenario, it could be that the zanpakuto has a mind of its own. It takes control of Naruto and forces him to attack Kakashi. The zanpakuto might be from a different dimension and is trying to create chaos in the Naruto world. Kakashi would have to rely on his ninja skills and his knowledge of various jutsu to counter Naruto's attacks and find a way to free Naruto from the zanpakuto's control.