Horse riding

[Bettyboo22]

Not sure what catogry this is supposed to be in so I will post it here ( sorry ) :-). I have a voucher entitling 3 people to go a horse riding the voucher says ages 4-16 all abilities. I would like to take my sister and cousin who are complete novicies with me ( I have been riding half a year) , but my dad thinks that it isn't sutible for them. Am I being unfair by asking him to let them come or do I have a fair point ?