Rahul you don't need to worry about the different solutions released by different coachings. Official answer key for this JEE Advanced 2018 paper will be released by IIT Kanpur on 29th May 2018. Then you can go through your optical answer sheet and match all your answers and calculate your final marks. Even after that if you find any error so you will have two days time to report the error. 

And you don't need to worry if there is some error in any of the question (which hasn't been found by any coaching yet) or if more than one pattern of answers are correct so it will be mentioned in the answer key. Last time in 2011 when IIT Kanpur conducted this IIT-JEE exam and there were errors in 4-5 questions so IIT Kanpur allotted marks to everyone in a few questions and in a few questions it gave marks for more than one pattern of answers. I cleared JEE exam in 2011 so I very well remember it.

Feel free to ask if you have any more queries. All the best!!