congrats

nah, you really can't tell twins from a HPT
if your morning one was bright, it's possible you just have as strong a line as that test makes
you're what, 16 dpo? (I'm 2 days behind you)
your hcg might just be high enough that an increase can't be seen on the test, since the first test was already as positive as postive gets

also, different tests have different amounts of dye, supposedly...I keep reading that you shouldn't freak out if your lines don't get darker for this reason
a few months ago I had a nightmare (no kidding) that I was pregnant with twins...it was bad
twins would be a huge blessing, but I'm sure my reaction to finding out would be to cry