I think you should pick whichever one (or even two) you find the most interesting and in which you can excel. The specific major doesn't really matter that much. Your GPA matters a lot more. My BA was in Anthropology & Latin and I got a minor in Archaeology, so not exactly the typical kind of BA one gets before going to law school. Don't focus so narrowly on your end goal of going to law school that you don't take the chance to experiment with classes from different departments that sound interesting to you, even if they don't relate to your goal. I took a lot of electives that just sounded interesting to me like sign language and a class about juvenile delinquency. I actually started college as a Biochem/Latin major. I took Anthro my 1st year and found it much more interesting than Chemistry, and then switched majors. Anyway, don't box yourself in so much that you don't explore your options in college.
Oh, as to why it has taken him 5 years. During the brief time I was a biochem major, I learned that 5 years was not uncommon for that degree. So, the fact that your brother was able to change majors so many times and graduate in 5 years with a biochem degree is actually pretty good. He must have already been taking a lot of the classes toward it because (at least where I went to school) you had to take through Cal III, chem, organic chem, biochem, other chem classes, lots of bio classes, etc, which can easily take 4 or 5 years when you already have a lot of other required courses for the university itself.
I heard that a good SAT score will lead to a LSAT score because LSAT is logic and SAT is also logic (especially for the critical reading)? It sounds kind of absurd because its a pre-college level test but I heard this from a lot of people who took their LSATs and are heading for law school