Start with what you know.
The profiles indicate that some of your grandparents are still living. Have you asked them about themselves, their parents and other family?
Then take what you think you know about family, and search in FamilySearch (it's a good place to start because it's free and it has a lot of good content) for records for your grandparents. Enter name, a range of dates (for example if you think someone was born in 1928, I'd enter 1925 to 1930 for the birthdate, to catch records that have the date a year or two off), and place names, and see if you can find them. Some types of records will contain names and dates for parents, siblings, etc., which should help you start WikiTree profiles for them, and give you information to use in additional searches.