If I have two tabs open, will tab one route through Alice to get to Bob and will tab two also route through Alice to get to Dave?
In Tor Browser, isolation is performed by the first party domain. So, if tab A is for
bob.com as the domain and tab B is for
dave.com, they will use distinct circuits.
However, if tab A and tab B are both for
bob.com then they will both use the same circuit.
Note that a circuit conists of 3 or more relays, the first relay will stay the same over a long time period, this is your Guard relay (or a Bridge, if you use one). The other relays are subject to change on a circuit to circuit basis.
The answer is right here in official docs : you need to specify corresponding flag to SocksPort - IsolateDestAddr