Siblings must have the same Parents to be connected. If siblings aren't connected, that means their parents have duplicate records in the database (a separate record for each sibling). There are two methods to correct this:
1) You can delete the parent record from one of the student's tab (click the Red X located at the top left corner, next to the "Household" label) , and then the "select existing parent" drop down will appear. Select the correct parent from the drop down. Note: you can't delete a parent record if he/she has donations, so use Option 2 if there are donations.
2) Use the "duplicate check feature" by making a small edit to the parent's information (remove and add a letter back into the name, address, or phone number.) When the system detects two parents with the same name, address and phone, it will prompt you to select the parent that you want to keep. From the drop down, choose one of the options (Use Household 1 or Use Household 2. Either choice is fine.) The records will be merged and siblings joined. Note: make sure the parent record has a name, address, and phone number so that you can find something to match with.