As mentioned in the Apalis iMX6 datasheet, section 5.20 (https://docs.toradex.com/101770-apalis-imx6-datasheet.pdf); Apalis IMX6 supports 2x IPU (image processing units, IPU1 and IPU2) which can be used to connect 2x camera sensors.
The 1st camera sensor interface (IPU1.CSI0) is available as Apalis standard feature (8 bit YUV).
For 1st camera sensor interface (IPU1.CS0) pin details: refer Apalis iMX6 datasheet, table 5-59, 5-60, 5-61
The 2nd camera sensor interface (IPU2.CS1) is available as alternate functions of other pins.
For 2nd camera sensor interface (IPU2.CS1) pin details: refer Apalis iMX6 datasheet, table 5-62
In case you open to other types of camera sensors, I would recommend you to also consider MIPI-CSI (4 lane) interface, which can also be used to connect 1x MIPI-CSI camera with Apalis iMX6. MIPI-CSI signals are available in type-specific area of the Apalis module, thus you may not have to lose few standard features (as parallel camera signals are available as alternate functions of other pins). Using a combination of parallel camera and MIPI-CSI is also an option.
Please refer to Apalis iMX6 datasheet, Section 5-20.2 for more details.
Please check Apalis iMX6 Mezzanine and OV5640 camera module (schematics and datasheet) for MIPI-CSI interface reference design:
Let us know if you have any questions.