[CRM 2015] Sharing records between different business units

Hi,

We have the following business unit setup:

BU A - root Business Unit

BU B, C - child Business Units to BU A at the same level

We want to share all records of an entity type (i.e. Account) between business units B and C, is there a way to do this without using Teams?

Can this be done strictly through using security roles?

Thanks.