If you know the chemical reaction yields alcohols, there should be adequate references to suggest which alcohols. You can buy small amounts of alcohols to use as standards, then inject individual compounds of increasing chain lengths into your GC.  Chemical standards suppliers used to sell mixed samples.  You could also derivatize your alcohol samples with a silylating agent and see which peaks disappear, and which new peaks appear.    

I agree with David, you must have standards to confirm your peaks. Did you do with GC-FID or did you do with GC-MS? If you did with GC-FID, be careful the identical Rt does not means 100% identical compounds (alcohol), for this purpose you should try to analyze with at least with 3 different  conditions to confirm their identities. I recommend you use GC-MS or GC-MS/MS to analyze your possible alcohols. Good luck! 

I also agree with the above suggestions, you can't  be certain what compounds  they are untill you run the standards under the same conditions. But your alternative would be to run GCMS of the same sample to identify the alcohols.

I really appreciate  to all who have given the answers and thank you very much. To Prof. Gunawan I (Airlangga University), I did analyse using FID and thank you for your suggestion. To prof Carlson, thanks to your suggestion for adding adequate references (alcohols) due to correct identification.

 Dear Prof Gunawan, do you know where I can analyse my  sample using GC-MS/MS ? I really appreciate it and look forward to hearing from you.