When is it legal to ask your tenants to move out?

[Kat Hughes]

Hi!

We own a multi unit property in Los Angeles Ca.  Front house and a duplex in the back.  The duplex in the back has been rented since 2012 by amazing tenants who have been paying their rent on time every month.  However, we want to ask them to leave so that my brother can move into one of the units and my parents can move into the 2nd unit.  Is this ok to do?  What legal and valid concerns will the tenants have against us should they wish to sue us for asking them to leave?  And what if this is our true intent but my parents decide after asking the tenants to leave that they no longer want to live in the unit and we end up renting it out to new tenants?  Can the old tenants come back to us and say we tricked them into thinking it was for family reasons but actually not?

My dad recently had a health scare and we wish for him to live closer to us.  We live in the front house.  But the unit behind us is a two-story duplex and my dad is contemplating if that is right for him or not.  And that's why we're not sure.  We would like for him to move in but we're not entirely sure yet.  

Would appreciate some advice, especially since CA laws are more tenant friendly than landlord friendly!