I have 51% in graduation and 65 and 67% respectively in 10th and 12th, what are the chances of getting a top 4 IIM's and FMS Delhi?

FMS Delhi gives 50% weightage to the CAT score, which maximum weightage is given to the verbal section of the CAT. Class 10th and 12th are given 10% weightage each. If your 10th and 12th score is 60-75%, then you will receive a 5% score, and if it is more than 75%, then you will receive a 10% score. 

Your 10th and 12th score is low, but you can still make up things in the CAT exam, especially in the verbal section and your interview and SOP discussion, interviews at FMS has been given a weightage of 15%. Your graduation percentage is just above the cut-off of 50%, which might create problems for you in admissions, but yes, miracles do happen. 

If you score well in your CAT and interviews, there are chances. For other IIMs, the criteria remain somehow similar. All of them gives priority to CAT score and interviews.