To answer the original question, yes, if they are truly connected, BT+BHS and BT+BT are beam series. However, at level 8 the BT BT is not allowed. We have a girl who does a BWO+BT and the judges like it because its different.
Regarding the question about series finishing on the beam, for all JO levels requiring a tumbling series on the beam, the series MUST start AND finish on the balance beam.
The BWO+BHS+BT dismount gets credit because of the BWO+BHS (that is the series that starts and finishes on the beam - the fact that she can connect the dismount out of it is pretty awesome). IF she fell in between or didn’t connect the BWO and BHS, but did connect the BHS+BT dismount, she would NOT get credit for the SR of a connected acro series.