Combine all the individual monthly sheets. (Jerry Beaucaire has a macro to do this if manually is too tedious). Because you specify “need to maintain as monthwise separate sheets”, from the combined sheet each month filter each month for the required month and then copy the result to a new sheet with an appropriate name.
Create your summary with a pivot table. This is much more versatile for analysis and altogether avoids the need for formulae to achieve the result you want. If you want the summary for each person on a separate sheet (“needs to be summarized on single sheet for each person from different sheets”) filter the summary and copy the result to separate sheets. However if you mean summarized for every person on a single sheet there is no need for filtering and copying - the pivot table is sufficient.