Karnataka

First of all, IISc actually doesn't offer B.Tech at all. It offers Bachelor of Science (Research) which is a four year programme. For B.Tech you must go for any other colleges.

Yes ofcourse. You are eligible for applying for B.E. In civil engineering.

The minimum eligibility criteria of various courses offered at Alliance University Bangalore is 10+2 with minimum 45% of marks for general and 40% for reserved categories. Hence you are not eligible for any course if belongs to general category.

NIT Surathkal is very difficult. However you can tryout the following Engineering colleges of your state.
1. HKBK College of Engineering, Bangalore
2. MVJ College of Engineering, Bangalore
3. CMR Institute of Technology, Bangalore
4. KLE Technological University, Hubballi
5. Ballari Institute of Technol

Your son KCET rank is really decent. Based on the KCET rank, your son can get the following engineering colleges in asked category under Karnataka domicile.
1. PES University (PESU)-CSE& ECE
2. RVCE Bangalore-Mechanical
3. Dayananda Sagar College Of Engineering -Aeronautical& Telecommunication
4. BMS C

You can expect a rank under 5000 easily. You will be treated as a general candidate itself because you are a non Karnataka student.