I'm sorry about your granddad.
No, it wouldn't make you a selfish girl at all.
The best way to take the decision is to anticipate the future: in a year from now, how would you be at peace with yourself: to have attended the funerals or not?
If you decide to go on the planned date, you could "attend in thoughts" the funerals, by praying from afar during the time of the ceremony. Maybe find a church in Mexico. I'm sure your granddad would appreciate.