Huge mess, not sure were to start?

Hi! I hope someone can tell me what to do...

These are the facts:
1) My husbands grandfather died 02/12/2013. He was resident in Logrono in Spain. He had a Spanish will.
2) The will declares that he disowns his children and wants to leave everything to some of his grandchildren (2 excluded) and 2 great grandchildren (descendants of a deceased grandchild).
3) The great grandchildren are not named, only mentioned as the grandchild's children. One carries the father's name, the other does not.
4) Two of the grandchildren mentioned in the will are resident in South Africa, the rest are in Spain.
5) There is no executor mentioned in the will.
6) There is a property and money.
7) The property is also in the name of the grandfather and grandmother who are legally separated.

So, we have a copy of the death certificate and the will from Madrid.

Do we need to appoint an executor to execute the will or does the notary who wrote the will execute the will?

The surviving children (legal heirs) do not want to contest the will, does that mean the will can be executed as stated in the will?

My husband is the oldest grandchild and so everyone is expecting him to sort things out but he is in South Africa.

How do the papers get sorted out if some of the beneficiaries are not in Spain?

I read that the inheritance tax must be paid within 6 months from the date of date by the inheritors. What happens if they don't have enough money to pay it?

We don't know where to start or who to ask, please can you guide us?