When there are two siblings in a family trust should they both be co- executors after parents pass.

Your parents can name whomever they want as successor trustees but are generally advised not to appoint co-trustees.  Co-trustees can be responsible for one another's actions.  In an already fractious situation, this could lead to more trouble.  The person who is not a trustee is entitled to annual accountings (in most states if 25 or older).  Most revocable living trusts distribute assets and terminate quickly after the death of the second spouse to avoid high taxes.  Your parents should discuss the particulars with their estate planning attorney.  It is really none of your business.