He can still continue with the parent sponsorship even while on EI as it is not considered social assistance. However that said, if the total 2014 income for 2014 drops below 2014 LICO requirement, it can jeopardize the sponsorship. The new rules states that the sponsor not only qualify the 3 previous tax years, he must also maintain yearly LICOs requirements during the entire Parent PR sponsorship until the parents land as PR.
So as long as your brother had a co-signer (wife) or picked up another job soon he should be okay. It is early in the year and he has 11 months to come up with the 2014 LICO requirement. So using 2012 LICO as a good indicator benchmark, he must have an income of at least 2012 LICO by the end of this year if not a little more.
Screech339