Yes it's essentially 'sponser my fun day out'.
Make sure you caught up the actual cost of the tandem jump yourself, and so all sponsorship money goes to the charity.
Yes there is a weight limit (around 16 stone, varies a little bit) and hell yes they make you jump on the scales. It's obviously exceedingly stupid to lie as it could be dangerous.
If you are right on the limit they might not take you unless there is a little bit of wind to help with slowing the landing down.
You are highly unlikely to die, but fat women do break their ankles more often than other people so work on your strength and flexibility because you need to be able to lift your legs for landing.
Why don't you do something that actually required some training and hard work rather than sitting in a plane and getting bundled out by the instructor? You basically do nothing. It's a lame way to raise money.
Dino Evidence please for the £1 to £14. I call bullshit on that considering on a sunny weekend in the uk in the summer the skydiving centres can do something like 2000 tandems with zero injuries.
I believe you might be thinking of an old study which was actually talking about charity static like jumps. Which centres are very reluctant to do now anyway ( charity jumpers have no intention of carrying on, fatter, unfitter, generally not as attentive as someone who actually wants to do a static line jump).