I am living in Germany with my family (my wife and daughter) as we have residence permission. We are Iranian, and would like to visit the UK for the next school holidays in Germany. How can we can apply for visa and what documents are needed, as our residence is Germany?
The UK runs a governmental website which contains plenty of information on the topic. It is complete and interactive. What you can do is use the dedicated tool to check whether or not you need a visa. In your case:
You’ll need a visa to come to the UK
The visa you need depends on your partner or family member’s situation.
They’re a British citizen
In most cases, you should apply for a Standard Visitor visa.
You should apply for a ‘Surinder Singh’ EEA family permit instead if you’ve been living with them in an EEA country other than the UK and they’ve been working, self-employed, self-sufficient or studying there.
They’re from elsewhere in the EEA
Apply for a family permit.
They’re from outside the EEA
Apply for a Standard Visitor visa.
This information includes both you and your wife's situation. You need a standard visitor visa to come to the UK and so does she since you are neither a UK nor an EEA national.