Ad coms read 40-50 essays a day. Do you think they'll be gripped by you whining about all the hard circumstances of your life? It's possible, IF you can present it in a well thought out way, that doesn't make excuses. However, I feel that 95% of the people that write these essays are really just explaining away/whining/making excuses for their low gpa. You'd be better off with an addendum, unless you can sincerely and maturely discuss your brother's life, what the loss meant to you, and work it in as A motiving factor to you, like to pursue dreams, etc. But making that the main point in your essay is a mistake. That's what addendums are for.
Take the PS as your chance to let ad coms know who you are and see something else about you and why you want to go to ls, not why your gpa sucks.
(can we tell I've been reading PS books, getting ready to write mine? You should pick one up. If nothing else, it will elaborate on what NOT to write...)