Depending on the age of your children you're going to need 3/4 bedrooms, 1 for you, 1 for your parents and either another 1 for both kids if they're quite young and can share or 1 each if they're older. So 4 (living/3 bed), 4.5 (living/dining combined, 3 bed), 5 (living, 4 bed) or 5.5 (living/dining combined, 4 bed).
The general rule to work to for one person is CHF100 a day, but you should check with your canton's migration office on what figure they would consider adequate to support 5 more mouths. Each canton is different as depending on where you live can make a big difference in living costs. https://www.ch.ch/en/family-reunification-eu-efta/
However, you can only bring your parents over if they can prove they are already financially dependent on you. Who may apply for family members to join them and reside in Switzerland?
- Children or grandchildren who are under 21 years of age or who financially depend on the petitioner
- Parent(s) and grandparent(s), provided that they financially depend on the petitioner (they must prove that they were dependent on the petitioner before entering Switzerland).
I would be wary of uprooting your parents from everything they know and plonking them down in a strange country where they don't speak the language. They will feel isolated, have difficulty making new friends and will not be able to communicate with others easily.