You are right to be concerned. 100,000 is hardly sufficient for two people to retire on, especially if there is no additional income. You should steer completely away from financial advisors Their objective is to make money for themselves, not their clients. If financial advisors were any good at what they do, they would not be advising others, they would be too busy making money themselves, using their own personal funds.
If your grandparents will be retired, they will have plenty of time to do some research on investments. At their age, they can not afford to take risks with their money so they should consider some type of annuity that will return their principal to them along with any interest it earns over a fixed period of time with monthly payments to them.
Please do the best you can to keep them out of any "pie-in-the-sky" schemes that claim to increase their capital significantly over a short period of time.

