You need to know their routines. Observe them from a distance. Do either of them work? Are they dating anyone? Do they shop on a particular day? What time do they leave? When do they come home? Figure this shit out and it'll be easy.
Breaking in whilst either of them are home, is a bad move full-stop. If you are involved with these people, the chances are that they'll recognize who you are. This isn't the movies where one of the main characters puts on a mask and suddenly no one is able to recognize them. Your mannerisms, the way you walk, talk, stand, move, your voice (even when putting on a fake accent) will give you away. Even if they don't recognize you at first, subconsciously, you'll come to mind and they will figure it out sooner or later.
You want it done quickly and quietly. Low risk. Avoid them entirely. Breaking in whilst people are home and attempting to subdue them is unpredictable. Too many variables to plan for. Remove people from the equation and things will go much smoother for you.
Firstly, you don't want to be seen by any witnesses. Neighbors or passers-by etc are all a threat to you. Blend in. Become someone they wouldn't even stop to look at. Sneaking around in the dark with a balaclava may sound cool to a 14 year old kid, but you'll have the full attention of anyone, should they see you. The most likely outcome of which, is that they'd call the fucking police. Someone walking around during the day however, who is simply ignored by everyone, is much harder to trace. You're practically invisible.
Hire a truck/van. Park up near their house (not directly outside, but down the street, so far enough that you can still see their entrance). Wait for BOTH to leave. There must be a time eventually where both will not be home, even if for a moment. The minute they leave, you get to work entering the premises.
I'd dress like a workman. Think of a roofer. Tool-belt, baseball cap, shades. Gloves to mask fingerprints. Make sure that shit is filthy. Spill paint on an old pair of jeans. Throw dirt all over your boots. No one will question the fact that you have a crowbar. Keep either a dustmask around your neck, (a bandanna tucked in to the shirt so it's not noticeable also works). You can pull it up over your face as needed, to avoid being profiled by footage from any external security cameras. Bring one of those large worker's toolbags, so you can put their cash and the USB in. (Forget about fencing their computer, it's a retarded way to get caught, leave that shit behind). Double-up (or triple if needed) on socks and get boots that are too big for you, so any footprints left don't match up with your size. Carry a clip-board, if anyone was to notice the workman turning up at the neighbors home, people will presume you've got your work labelled on it and won't question why you're working whilst the occupants aren't home.