The validity of a test depends on many factors. Some relate to the intrinsic properties of the test itself. Others depend upon how the test was conducted and the way the blood sample was stored. In general I must say that Ganga Ram hospital has an excellent reputation and I would normally accept their reports implicitly. However, there is evidence that the NASBA-QT test is not equally sensitive to all subtypes of HIV-1 especially when the concentration is low (as in very early infection).
HIV-2 is found in India though not very frequently. Ideally in case of possible exposure it is better to test for both types of HIV. Until you are SURE that there is no infection (and the test report from Ganga Ram suggests that you are not infected) you do need to take some precautions. Please either avoid penetrative sex with your wife or be sure to use a condom. No other precautions are needed with the household and the other members are not at the slightest risk in any way. Behave and live as usual. The ONLY precautions you need to take relate to sex (and blood donation).
Tests for HIV are available at many labs. Please get it done again. The usual tests (based on antibodies) such as ELISA, rapid or spot tests should be done after 12 weeks of the exposure and possibly again after another 12 weeks. Even if you get one positive report please do not accept it as saying you are infected until it is confirmed by another one, or possibly two tests. If any of the tests are negative (even one) then please believe the negative report.