i) Lower berth possible in case of 45+ female and 60+ male passenger when travelling alone. Power of single booking. If more than one passenger but satisfying the above criteria, then try booking through two different forms.
There is a seperate lower berth quota for this category.
ii) Lower berth possible to the extent of availability in general cases, if choice ticked mark at the time of booking the tickets ... that booking only if one lower berth....
iii)...
more... Under peculiar circumstances, you can always request to the co-passengers for exchange of berths and such genuine cases, nobody refuses.
Wish you happy journey.