Gibson family have bought tickets to the christmas market there are four mothers, 2 grandmothers and 4 daughters what is the minimum number of tickets they need

We have six ladies and name them:

1,2,3,4,5,6

where 5 and 6 are the daughters of 3 and 4, 3 and 4 are daughters of 1 and 2.

Now,
1 and 2 are mothers of 3 and 4 = 2 mothers
3 and 4 are mothers of 5 and 6 = 2 mothers
1 and 2 are the grandmothers of 5 and 6 = 2 grandmothers
5 and 6 are the daughters of 3 and 4 = 2 daughters
3 and 4 are the daughters of 1 and 2 = 2 daughters
2 granddaughters 5 and 6

So now you have a list of 12 people ! ... 4 mothers, 2 grandmothers, 
4 daughters, and 2 grand-daughters ... and they all get in to the Christmas Market with only six tickets.  

Use a calculator basically