Hello Manuel;
The only difference between the 2 connectors you have selected is the presence of a "piggy-back" connector on the unit with a BB descriptor. See the images and descriptions from the Siemens Support pages:

The piggy-back(also known as "PG socket")is a secondary female Sub-D 9-pin connection at the back of the connector that allows a Profibus or MPI cable to be integrated temporarily to the network (practical for connecting a programming device for example).

Both of these connectors have a 90 degree angle connection, and a terminating resistor integrated in the housing.
I would recommend you purchase 3 connectors of the same type, without piggy-back (they are a bit less expensive), simply to make things easier on your first try. This would allow for a permanent connectioon of the 3 units.
Or if you prefer to disconnect your PG use 2 -0BA12- connectors and one -0BB12- connector so that you can plug in the PG to the permanent section (between the PLC and the OP) only when required.
To make things clearer (I hope) I have prepared a small sketch of the 2 options, see the attachment.

Then connect the 3 with appropriate lengths of Profibus-DP cable as required.
Hope this helps,
Daniel Chartier

Edit:
First question: what are you planning to use to connect the PG to the other units on MPI? A PC Adapter, a Profibus interface card (such as a CP 5611) in the PC? If you have a connection to the PLC already functionnal, you onl;y need the -0BB12- piggy-backplug to connect the pG to the network.
Second:question: you do not mention the model of OP you are connecting to the network. Sometimes these units do not allow the space for a 90 degree Profibus connector due to their particular layout. The recommended type of connector is described in the technical specs of the unit (or in the operating manual), so please check them out before purchasing the connector. It would be frustrating to recieve them and find out afterwards that you need another model (this is one reason there are so many different models of Profibus connectorsn offered).
D.C.