Design

Yes, you can get the admission in interior designing and admission will be based on entrance exam score in any institution. Some institutes offering this course are IIFT-INIFD-Institute Callegari Milano-Aesthetic Institute of Design -Raffles Millennium International etc.

It's 9.5 lacs for 4 years. Refer to prospectus for more details at page number 69.
https://nift.ac.in/sites/default/files/inline-files/Prospectus 2019 compressed. Pdf.

Yes, anyone who has cleared the 10+2 from any recognised boards, with no other bachelorette degree is eligible for B.A. Programme from DU-sol.

Fee structure for B.Sc in fashion Rs. 10,000 to 1 lakh per annum, interested candidates can apply directly to the college.

NIFT doesn't provide any Diploma courses all you have the degree courses to choose from. Courses provided by NIFT:
Undergraduate (UG) Programs
Bachelor of Design (B. Des) Bachelor of Fashion Technology (B. F. Tech ). Postgraduate (PG) Programs
Master of Design (M. Des) Master of Fashion Technology (M. F. Tech). Master of Fashion Management (M. F. M).

You can check this on their website
https://www.amity.edu/admissions-scholarship.aspx

It depends on the Curriculum of the college.

Various colleges are providing PG Diploma in Interior design such as: Bhavy Shimla School of Design
Gurgaon, GD Goenka University - GDGU, Gurugoan
School of Design and Visual Arts, Apeejay Stya University, Gurugoan
These are some best options to go.