My husband and I are busy and decided to keep our second son at his grandparents' for his first two years. Will this impact our relationship later?

Why do you want to deprive your son of his parents' love and affection? Grandparents cannot take parents place. There are many working couples who spend quality time with their children. Children just need the parents around. What will change after 2 years? Of course, there are couples who are happy with this arrangement but personally I would say No.