半 Bàn is 'half':
Imagine a buoy half above the water.
伴 Bàn is 'accompany':
The element on the left is a form of 人 rén 'person'.
判 Pàn is 'to judge':
Common word: 批判 pīpàn 'criticize'
The element on the right is a form of 刀 dāo 'knife, sword'.
叛 Pàn is 'betray':
反 Fǎn means 'against'.
Common word: 反叛 fǎnpàn 'a rebel'