Hello Sebastien,
You needn't two ADC_LDD component in your project to measure two channels. Use one instance of ADC_LDD in your application and add one channel into the ADC_LDD component (so you have two channels in the ADC_LDD component that can be measured), see the following screenshot:

You can also enable static sample groups, define one sample group for each channel and use methods SelectSampleGroup and StartSingleMeasurement for measuring these channels (software triggering). Or you can use (hardware) triggers, see the Trigger group in the Compnent Inspector.
For details see the help of the ADC_LDD component. There is also an example of typical usage.
Best Regards,
Marek Neuzil