First, you need to request access to the "managed" people from your brother. On your Family & Friends list, click on the 'Add a Guest' link near the top. You will see a list of your Friends' friends, including profiles they manage. So you should see your brother's wife and daughter on the list. Select those two "managed" people and click Done. An email will be sent to your brother to approve your request. When he approves it, you will see them in your list.
Here are a couple of notes. When your first make your request, the
MDE system will create "dummy" accounts for the newly requested people, along with the comment that YOU manage their account. If you go into their account, you will see some information about them but not their tickets or reservations. Do not do anything at this point with these accounts - they are dummy accounts. When your brother approves the request, these dummy accounts will update with the real information, and it will switch to saying that your brother manages these accounts (which is correct). Then, you can make all the plans that you want.
Second, if you cannot see the names of your brother's wife and daughter when you do the link above, your brother needs to change the privacy setting on his friends and family page to allow everyone to see the list. This link is directly below the list friends.
Third, if you are planning on purchasing a Memory Maker package, make sure your brother goes into his wife and daughter's profile and clicks on your name (you now show under each person separately as being their friend) and ensure the checkbox for you being able to see their Fastpass photos is turned on.