How to get rid of lots of soql queries using maps - triggers

Question

Im finding it really hard to understand maps, I have read lots of examples but they always seem not to relate to what I need to do - I've just about understood how to use oldmap.trigger in a very simple use case.
So anyways I have a trigger on a object Data_ProtectionIA , its parent is Data Agreement, and then its parent is Data request.
I need to update Data agreement and Data request when DPIA gets updated, I have the below so far which I know is a very long winded way to do it, but now I also have to add further updates for when DPIA gets updated to something else and for me to do this like I have done would mean doubling this code again when it is already unnecesarily long.
If someone could please simplify this code into maps then I think I would be able to understand maps properly, I just cant find examples of what I need to do. Many thanks in advance
(So at the moment I am getting the grandchild record and then creating a list of parent records to loop through and then getting a list of all their parent records and then looping through that. - even if you could just show me from child to parent (not even, child parent to grandparent that would be very helpful)
public static void setDRStatus(List<Data_Protection_IA__c> dpia, Map<ID,Data_Protection_IA__c> oldMap ){
List<ID> childDAID = new List<ID>();
for(Data_Protection_IA__c pDA: dpia){
if(pDA.DPIA_Status__c == 'Fully Approved' && oldMap.get(pDA.Id).DPIA_Status__c != 'Fully Approved'){
childDAID.add(pDA.DataProcessingAgreement__c);
}
}
List<Data_Agreement__c> childDA = new List<Data_Agreement__c>();
ChildDA = [Select id, Data_Sharing_Status__c from Data_Agreement__c where id in:childDAID];
List<Data_Agreement__c> listToUpdate = new List <Data_Agreement__c>();
List<ID> dAId = new List <ID>();
system.debug('ChildDA'+ childDA);
for(Data_Agreement__c cda : ChildDA){
cda.Data_Sharing_Status__c = 'DPIA Fully Approved';
listToUpdate.add(cda);
dAId.add(cda.id);
}
update listToUpdate;
List<Data_Request__c> dRList = [SELECT id, Data_Sharing_Status__c,Existing_Data_Agreement__c
FROM Data_Request__c where Existing_Data_Agreement__c in:dAId];
List<Data_Request__c> listToUpdatedr = new List <Data_Request__c>();
system.debug('DRList'+ dRList);
for(Data_Request__c dr :dRList){
dr.Data_Sharing_Status__c = 'DPIA Approved';
listToUpdatedr.add(dr);
}
update listToUpdatedr;
}
----------------------------------------
Here is an example I had previously tried
So I started following an example and got to here
Set<Id> daIds = new Set<Id> {};
for (Data_Protection_IA__c p : dpia)
{
daIds.add(p.DataProcessingAgreement__c );
}
Map<ID, Data_Agreement__c> m = new Map<ID, Data_Agreement__c>(
[select id, from Data_Agreement__c where id in : daIds]);
list<Data_Agreement__c> dAupdates = new List <Data_Agreement__c>();
list<Contact> contactupdates = new List <Contact>();
for (Data_Protection_IA__c p1 :dpia)
{
m.get(p1.Data_Agreement__c) = 'DPIA Fully Approved');
}
but at the last line I think this map is tying to get the field Data_agreement from dpia object, but there is no data agreement field on dpia object. as dpia is the child. there is only a field for dpia on the data agreement object