welcome, and hello
guppies are my favorite fish, i have kept them and bred them many times. i have just returned to fish keeping from a 5 year break, but i can tell you not to worry so much guppies are soo easy.
what exatcly is your first question?
if your females have been kept with males at all at any point they are pregnant, female guppies can store sperm for months, they usually drop fry every 25-30ish days.
and the second question well nipping or chasing is mostly normal behavior , unless it is causing ripped fins or one fish is predominately very aggressive and harasses another fish none stop, then i would remove that particular fish.