1) I'm no expert on GSE
2) It depends on the individual product and what concentrations of chemicals like benzethonium chloride it contains.
3) There isn't any good research so I doubt anyone really knows anyway.
On a more positive note, Dr. Leo Galland has been prescribing Grapefruit-Seed-Extract for over 7 years, so I guess he considers it relatively safe.
If 15x3 drops is a recommended dose of your Grapefruit-Seed-Extract product, then hopefully that is a safe dose. I don't know enough to say it isn't. But I can't reassure you that taking such a dose for a long time may not have some negative health consequences.
If GSE works for your Lyme disease and parasites as well as Candida, then I can understand if you continue to take your GSE even if there is a small safety risk.