First, your grandparents who bought the property in 1949 are obviously still living. correct?
if so, then the only property you will get are those properties owned by your parents when they died. Your grandparents' properties are their own while they yet live.
However, when your grandparents eventually die, as all human beings do, then their properties will have to go to their heirs. Your grandparent's heirs are of course your parent's siblings. As you said, there are 4 siblings. If A and B died in 1941, A being your father, then the remaining living heirs of your grandparents are C and D.
Having predeceased your grandparents, A and B's estates will still get their share of your grandparent's properties. Hence, if A is your father, then A's heirs (you and your siblings if any, or any surviving spouse if any) will only get what A would have gotten had he been alive. So kung may mga kapatid ka, you will have to divide with them the properties that A would have gotten.
With regard to the property bought in 1949 by your grandparents, hindi pa sure kung makukuha ninyo yun. Once your grandparents die, there will still have to be distribution and partition of the estate among the heirs, hence YOU MAY OR MAY NOT GET the land or a portion of the land bought in 1949.
Things you have to know are the following:
1. do your grandparents have a will?
2. if yes, then whether or not your father (A) wll get the land, depends on what is stated in the will.
3. if there's no will, then you may enter into extrajudicial partition with the other heirs of your grandparents, wherein you may lobby in getting the land bought in 1949.
Hope this helps! good luck!