Friends, family, allies can all cause conflict because of opposing goals.
As writers, we can mine this conflict in our stories.
Why do we constantly look for sources of conflict? To cause trouble for our main characters.
Why do family members, true friends and coworkers want good things for us. They don't want to stab us in the back. BUT, sometimes good intentions cause problems.
Brothers and sisters can have OPPOSING GOALS than our characters. Friends can create fireworks when they block our MC from getting what he/she wants.
What if they want the same thing? SHARED GOALS can cause conflict, too. Working together towards a shared goal can cause competition in how to accomplish them.
ENVY makes allies into frenemies.
What about inserting WEAK MOMENTS into the scenes? Everyone has them, so writers can use the emotion behind these times to ensure tension. For example, how many of us have cancelled plans with friends when a better opportunity comes along? These poor decisions can create huge complications down the road.
So, using friends and family for conflict can really add to our plots.