In what order were they born (oldest first)

Question

Hari (H), Gita (G), Irfan (I) and Saira (S) are siblings (i.e. brothers and sisters). All were born on 1^st January. The age difference between any two successive siblings (that is born one after another is less than 3 years.                                                                                                                                                                  

Given follow facts:

1. Hari's age + Gita's age ? Irfan's age + Saira's age
2. The age difference between Gita and Saaira is 1 year. However, Gita is not the oldest and saira is not the youngest
3. There are no twins

In what order were they born (oldest first)

      (a) HSIG                                                             (b) SGHI

      (c) IGSH                                                             (d) IHSG