having been an only child it's hard for me to understand sibling interaction - I seem to be a little to sensitive to their conflicts.  I'm working on this but it's really hard for me to handle it in a manner that is helpful.  It's mostly between the older two, but on occasion there is a little bit between the middle and youngest who are over 9 years apart. 

I often worry what will happen when the girls are older.  The youngest will at some point have to know the truth about her biological father and about what happened.  I can't even imagine how we will all deal with that.  It scares me.

Luckily the older too don't harbor or don't seem to harbor any ill feeling towards their younger sister for her origin.