I have compiled the box office gross collection of Bollywood on yearly basis since 1994 and compared the contribution of Khans in that. For the purpose of showing the numbers over the year, I have adjusted all the figures at 2019 prices.
The year having less than 25% from Khans is in red, between 25-40% is in light green and over 40% is in dark green, which has happened only once i.e. 1995. The best year in term of % share for Khans is 1995 while the worst being 2018.