Electronic – Meaning of FB symbol in schematics

These are multi collector (or multi emitter) bjts. Their operation is quite similar to the normal ones.

Multiple emitter bjt's do not conduct only if all the \$V_{BE}\$ are below \$V_\gamma\$, it is a sort of wired AND. Multiple collector bjt's collectors total current is set as usual by \$I_B\$, and if all the collectors are the same size (area at silicon level) the current is equally split.

Multi emitter bjt's are usually used to close some sort of feedback from following stages, maybe avoiding the bjt to saturate, or in logic input stages where the logic funcion is implemented directly by the wired AND, such as in this TTL AND input stage:

Multi collector bjt's are useful in IC's since it is easy to match the ratio between the collector areas and split a polarizing current in precise ratios, as in the uA741 output stage polarization (\$Q_{13}\$ here):

At solid state level to add an emitter you simply add an emitter diffusion:

For a multi collector you just need more than one collector contacts.

I'm not aware of a standard symbol for a pressure sensor.

Usually, it's drawn as an IC.

It's a good idea to indicate in the schematic that this is a sensor, and therefore something special. You can make a text block next to the symbol saying what the sensor is sensing. If you know what kind of sensing element the sensor is based on, you can draw an icon of the sensing element in the schematic symbol. If it's a MEMS pressure sensor like yours, you can draw a bridge on it. (Another example. If you know that some other sensor is based on a phototransistor, you can draw a phototransistor on it.)