For every empty seat that goes off into the park there is one disappointed person left behind. So, if you are in a jeep with 3 spare seats they will want to fill those seats
The permits are all signed off individually against ID,
a.) to make sure all permits are legitimately purchased, and
b.) To make sure of fair play.
Only so many permits are allowed each day, and only so many jeeps are permitted, and as you are finding out, they could sell those places 10 times over.
There are 6 seats available in each jeep, so if you only want 3 seats, that leaves 3 others.
If you have 6 permits all with different names on, they wont try to fill those 3 seats because they will think there are 6 persons already in the jeep.
But whos names will be on those 3 other permits ?
The park officers are'nt so much green, as they are cabbage looking
IMVHO Ranthambore is'nt worth the hassle, but everyone still clambers to get there.
I much prefer Corbett anyway, and there is no problems getting private jeeps there. It is a different world completely.
I am sure a travel agent will get you what you ask for but at what price ?
if they ask 1500/- x 6 = 9,000 /- thats an all day safari in Corbett
1500/- is the cost though it seems