Hello,
Yes, your brother can file IT Returns. Either ITR - 1 or ITR - 3 in case he wants to file Balance Sheet or ITR - 4 on a presumptive basis.
For your Cash Deposit since it is done on a regular/ early basis is not a problem if you would have deposited the entire amount in one go it would have been a big problem.
Make it a point to deposit regular sums every month than depositing in one go, it will help you save all the hassle and inquiry part.
Trust this clarifies your query.
Feel free to call / get back in case of further clarifications.
Thanking You.
Regards,
Rohit R Sharma
BCOM, FCA, LLB, CERT. FAFP