'Douse' (which rhymes with 'house') isn't a particularly useful or common verb. The most usual collocation is, if you want to destroy something, you can 'douse' it with petrol before setting it alight. I can't think of another common use of this verb. I've never used the word in my whole life, and nor have most native speakers, I suspect. You really don't need this word. 'Splash' and 'squirt' are 'éclabousser' and 'gicler' in French. As far as I know, the distinction is the same, isn't it? 'Splash' involves a larger amount of water, such as when you're standing at the side of the road in wet weather, a large vehicle comes past at high speed and soaks you. By the way, 'soak' or 'drench' ('tremper' en français) are far more useful words than the comparatively rare 'douse'. 'Squirt' involves a finer jet of liquid, usually forced out of something, like a water pistol or a washing up liquid bottle, for example.

Douse: drench something in water. Soak it. Lots of water. Splash: you can splash someone by swiping your hands through the water and into someone. A splash is more like a small amount of water hitting its target. Squirt: think of a water pistol. The water squirts out. I hope this helps.