I have 10-78%,12-74% and graduation-49.78%. I also have 30 months of work in my family business.Can I still have a chance of fetching a call from XLRI Jamshedpur through XAT if I score more than 99.5?

Though 30 months of work experience will add value to your MBA journey, XAT gives only 15 % for your academics and work experience. The chances of getting a call at this percentile is pretty high but it would also depend on your sectional cutoff; XAT usually gives a high weightage to your decision making score. 

XAT eligibility criteria do not require any minimum percentage in your undergraduate to appear in the exam but if you do get the interview call, the panel might ask you questions about the low score in your graduation. Make sure you give the honest answer but try to be smart with it. They are always looking for answers that show your potential and how you cna present even the worst things about your CV in a positive way.