Self charging wood-gas camping stove using thermoelectric module/modules
You can connect the TEGs electrically in series or in parallel. However, if they are not all at the same deltaTemperature, then there will be some inefficiency.

Either method would work, but using a DC/DC converter will allow you to extract some energy from the TEGs at nearly any deltaTemperature;if you just connect in series, and don't use (much) electronics, you'll only deliver power when the TEG voltage is > 12 V, and any V above this is 'wasted'.

Using a boost DC/DC in this type of application isn't trivial if you are trying to extract maximum available power from the TEG. If you are not careful with the control loop, you'll collapse the supply -- need to use MPPT tracking.