Your b/f should supply a letter of sponsorship giving information on either his immigration status or if British Citizen etc.
Also he needs to give a brief explanation of the relationship between you, the purpose of the visit and it's timing and also where you will be staying.
If your sponsor (b/f) is going to provide financial support for you or if he is going to pay for your travel expenses etc then he will need to provide evidence of his ability to do so for the duration of your planned trip. This will mean supplying supporting evidence such as 6 months bank statements and payslips and/or evidence of sufficient cash savings.
The accommodation will need to be outlined of course, but this will not hold the same level of importance for a visit visa as it would for a settlement visa.
It will be up to you/your b/f/your b/f's brother to decide and agree the place where you will stay. Wherever you finally decide to stay it's advisable to show that you have permission from the landlord(s) if it's a rented property. That applies to both your b/f's caravan and/or his brothers house. The brother of your b/f will also need to confirm his knowledge and his permission for you to stay there if that's what is finally decided. You will not need to secure any other special permissions, but proof of address may be needed (such as utility bills, bank statements etc).
The circumstance you mention appear quite complicated and will need careful management and a good supporting sponsor letter.
Please do not make any visa application that includes false information.
Doing that would severely impact any further visa applications.
Originally Posted by Terpe
your visa goodbye 
