Legal Entity and invoicing

We have 2 legal entities with one Operating Unit.  We have emp1 working for LE1 and emp2 working for LE2.   LE1 has project1 and LE2 has project2.  If emp1 works on project2 and emp2 works on project2, how do GL accounts get updated with costing and billing information?  We want to avoid LE1 invoicing LE2 and vice versa.  What type of setup is required to avoid LE's having to invoice each other and GL accounts getting updated accordingly.

Thanks in advance for your response.