Each profile can be set to use Kinect login separately. So if you only want you to be automatically logged in you can set that as such by going to settings->sign, security, and passkey->kinect sign in.
You can also do that method to calibrate the Kinect so it recognizes you or the "distracting" user better. Unless you are twins... this method should work.
TL;DR: Technically it's possible to acquire everything without paying a cent. It will just take a long time and a lot of work.
The Magic Keys you need to unlock lockboxes don't drop at all; the standard way to obtain them is by paying 125 Zen on the C-store.
Sometimes they're sold on the exchange by people who have money to burn and need the gold, but that's not a guarantee. However, if you're willing to put in a lot of work, you can get as much Zen as you need without ever paying a cent...
As user108818 tried to point out, there is a player-driven exchange market that lets you exchange "astral diamonds" (the refined kind, mind) for Zen (the PWE C-store currency) or vice versa.
The exchange rate is player-driven and fluctuates strongly depending on what people are willing to pay.
You earn "unrefined astral diamonds" through various forms of regular play, and can convert them to "refined astral diamonds" at a set limit per day (which is why there's a buyer's market for astral diamonds as well).
As of the current writing, and assuming the PC and XBOX versions have the same account, the exchange rate seems to be roughly 480-500 astral diamonds for one point of Zen.
Best Answer
It is probably the melee damage amounts:
So yes, your targeting does affect the melee in SW Battlefront 2015, unlike most other games. This is also never communicated to you by DICE in any documentation or in-game tutorials or tips.
(Keep in mind, mediocre netcode settings that DICE uses also mean sometimes the melee just misses when it appears like it shouldn't, or vice versa for the opponent. Not much you can do about that since they lock down all the settings unlike most other good games, for example games based on Valve's Source engine. But if you have a decent, stable internet connection, this doesn't happen too often. If it takes a second hit, the first was most likely a body shot.)
However, why you are dying in melee battles might be other issues. ;-) If you sneak up behind them as you say, hopefully you should be able to hit them twice before they notice you unless you do something else to give yourself away, or they have buddies, etc.