XAT

You can't apply, when you are filling the form there is an option in the form itself so you missed that chance, and you can apply for other colleges affiliated to XAT.
All the best!

You can go for the books of McGraw Hill publications.

The cutoff percentile for different exams is different every year and changes every time according to the exam. There is no fixed cutoff. Last year cutoff for CAT- 86 percentile, XAT - 78 percentile and CMAT - 96 percentile
For more information refer brochure:-
https://www.somaiya.edu/media/pdf/PGDM_Admissions_Brochure_2017-19.pdf
Online Application Form:-
http://simsr.somaiya.edu/simsr/adm/pgdm17/onlineform/login.aspx
Placement Report:-
https://www.somaiya.edu/media/pdf/Placement_Report_2015-16.pdf

Admission Open for MBA(RM) 2017-19 batch, Two-year full time residential MBA(RM) Programme KIIT School of Rural Management, KIIT University,
For More Information see www.ksrm.ac.in/web

You need to score above 600 in MAT and you may be eligible with more than 65 percentile in XAT. Although, you can also get admission through CMAT score of 200+.

IIMs consider only CAT for admission to their MBA programmes they do not accept any other management exams.

Yes the best score of CAT, XAT & CMAT will be considered for admission.

The XAT cut off for the 2016-18 batch was 80 percentile. This cutoff is however not fixed and could be different for the 2017-19 batch.

Yes it is very much important to take these exams. Actually when you prepare for these exams you get to know and analyse things in a better way or it will be accurate to say in a logical way. That is very much required in a corporate world. So these exams test your reasoning and analysis capacity. So it is better you secure your admission through these exams. It will benefit you in long run.
Best wishes!!!

Yes you can apply through both, the cutoff is 99.96 percentile.