You can still allocate the shared policy even if you file separately. Your mother and brother will need to report the same allocation on their returns. Typically the percentages would be split three ways, but you can split the allocation in any manner you wish, providing you all agree, as long as the percentages equal 100%.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"