I want all pregnancy_pp cases whose grandparent case_id is the same as the family_id

Without rooting the device I'm not sure of a good way of making any folder read only.

One option could be to place a .nomedia file in the folder where the multimedia is located. This will prevent Android from scanning the folder for media and hence it won't show up in any albums etc.

I'm assuming in this case that you've loaded a the member case into your form, and that you can load the member case ID id into

/data/member_id

What you want to get is:

The count of all member cases which are children of this case's parent, for which the member case has the property mm_is_in_tb_treatment = 'yes'

For now we can create a new hidden value to store the parent household's case ID, since it'll make understanding the full query below easier.

New hidden value: /data/parent_id:

instance('casedb')/casedb/case[@case_id = /data/member_id]/index/parent

All cases which are children of that parent would be referenced as:

instance('casedb')/casedb/case[index/parent = /data/parent_id]

You can now add your new filter directly to the end of that statement and introduce the count

count(instance('casedb')/casedb/case[index/parent = /data/parent_id][mm_is_in_tb_treatment = 'yes']

If you wanted, you could further specify that you (for safety) only want to include children that are member cases and which are open. You can also collapse back the parent ID reference if you want a one-line expression:

count(instance('casedb')/casedb/case[@case_type='member'][@status='open'][index/parent = instance('casedb')/casedb/case[@case_id = /data/member_id]/index/parent][mm_is_in_tb_treatment = 'yes']