If you are drilling a hole through 3 pieces, and you do not want to purchase a 12" "twist" (metal bit) bit to do the job, which would be the way to do it.
If you choose to use the shorter version, there is a way to do that too. Main thing is, is to use a twist bit since it is full round so to speak and once it starts in a direction, it usually will not redirect or change it's angle of drilling. It will take a few steps to accomplish the job.
First drill the hole all the way in as far as it will possibly go, hopefully a good distance into the second piece. If possible re-chuck the drill bit into the drill so it is barely in the chuck to maximize the drill depth, after you do the initial fist bore to get that "last little bit of depth".
Remove the first piece you drilled through. Using the hole that is started in the second piece, and re-chucking the drill bit in properly continue drilling using the hole that was started in the second piece as a guide. If that does not get you all the way through, use the same method mentioned earlier to get the rest of the way through.
If the holes are needed to go through the 7 1/4" height of the beam, you would be wise to get the long drill bit. If not take the chance and line the holes from either side the best you can, drill them in as deep as possible from each side and hammer the livin' crap outta them. They might make through... I have been that fortunate doing it that way too. It does blow out the wood a little bit on one side. That is the trade off, if it works....