activity led in an ir transmitter circuit
You should ONLY do that if the current required for the visible LED is the same as the current required for the IR LEDS. Which is doubtful.

If they are, you can calculate the R value based on the following formula.

\$R = (V_{SUPPLY}-V_{LEDS}-V_{CE})/I_{LEDS}\$

Where \$V_{LEDS}\$ = Sum of expected forward voltage of all LEDs at the required current.

Which position the visible LED is in series is unimportant if everything is local to the board. 

If the currents are different you would need to drive both in parallel as shown below, with their own series current limiting resistor.







simulate this circuit &ndash; Schematic created using CircuitLab