Again, you're thinking from your own perspective.
When you ask them why they are behaving negatively, you are sending
them a signal. You're telling them that you know that they are
behaving negatively towards you. See if they have a job problem or
personal problem then offer your help. Naturally, they won't tell
you, but it's important to let them know that you're there to
help.
Not asking them, not finding out the problem is the easy way out.
But it doesn't solve the problem. By not being candid, i.e. by not
asking them, you're just avoiding the problem. Just probe once in a
while, while not appearing to be pushy.
What's so hard about monitoring? Again, tell them frankly that they
are under your supervision and monitor. Tell them the target they
need to reach and their responsibilities. It's their responsibility
to hit the sales target.
2 weeks is still short. It's just like studying in a new class,
everyone starts to know one another slowly and then build
trust.
PS. I'm prefer western management more, hence most of the advice I
give are typically "in your face" and straightforward type.