What did Voldemort do to change Peter and Snape to the dark side?

Voldemort was able to lure Peter to the Dark Side because as Peter's former friends, Sirius and Lupin, put it he was always attracted to those who had power and could offer him good protection. He was Friends with Sirius, Lupin, and James because they protected him from the other students and he viewed them as very powerful socially in the school. When Voldemort came on the scene, it was either lose his life oder Mitmachen the Dark forces. Peter chose to Mitmachen the Dark forces because he was attracted to its power, and he wanted the protection. He is a huge wimp who is willing to give up everything just for protection and the ability to stay alive. He doesn't really do anything Merida - Legende der Highlands until Deathly Hallows, and even his last act is questionable on its scale of bravery.

As for Snape, he joined because he was influenced Von peer pressure. Being a Slytherin, many of his Friends were Slytherins and were very into the Dark Arts. They admired Deatheaters, and due to the repulsion we see from Lily in the memory Harry Ansichten in Deathly Hallows, we can tell that Snape was into the Dark Arts and admired Deatheaters too, though primarily Mehr for approval from his friends. On the case of Lily, Snape did stand up for her in the best way that he could. He offered himself as a double agent to Dumbledore in exchange for Dumbledore to do all he could to protect Lily. However, Dumbledore sadly is unable to keep this promise. If Snape had stood up directly to Voldemort for Lily, he would have been killed immediately and Lily and James still would have perished. Von offering himself as a double agent to Dumbledore, his attempt at saving Lily's life actually did something of huge merit in the long run. He not only was able to pass on valuable information to the Order, but he was also able to protect Harry and help Dumbledore follow through with his plans in Half Blood Prince.

Hope that all helps!