Each cam would need it's own HWK; one for each V3 (two HWK's) or one HWK for A129.
Most dashcams use between 500mA and 650mA for active parking modes. 1000mA = 1A, so from there you can figure out roughly what size battery you need to achieve a given number of hours use. Powerbanks and other Lithium technology batteries can be discharged to their specified rating. Lead-Acid batteries such as your car has (including AGM, SLA, and deep-cycle types) should not be discharged to more than about 50% of their rated capacity. So the advantage here is with a 2-channel cam which will go twice as long as two single cams, or give twice the recording time for a given battery size.
Worth mentioning here is the B1W, an older single-channel 1080p cam with the IMX 323 sensor. It does good day and night, and uses less power than any other dashcam made today. Not sure if it does motion-detect, most who use it for parking use it's low-bitrate FW. Also there's the Vantrue T2, which has an effective 'radar' type motion detection and in parking mode the cam "goes to sleep" using almost no power at all. With no triggering events this cam can give parking protection for at least a couple weeks without stressing your car battery. Unfortunately it takes a very long time to "wake up" when it detect something; 20 seconds plus, by which time whoever you wanted to capture may be long gone. For the right situation it could make a good choice but only then.
There are threads here about using LiFePO4 batteries and charging systems for dashcams and more. With these having power for a weeks parking time is no problem, but they are DIY completely and need good mechanical, electrical, and some engineering skills to use and the cost is high. Nothing to compare with these and you can get 10 years+ use from good components so they're actually a good value in the long run.
And motion detection. TBH it only works well in a few cans and few experienced dashcammers use it. Most of us prefer low-bitrate for parking protection as it is a far more certain method albeit more troublesome to find the clip you want should you need that. But at least you'll have something for sure, whereas with motion detection you might not have anything. In the dozen plus different cam's I've used, motion detect has worked well in only one and some others with the same cam who tried it didn't all have equally good results.
Parking protection with dashcams has always had issues attached and likely always will. It's better than nothing though.
Phil