No Soul Left Behind

1) Click the basket.
2) Click Animal Souls.
3) Click your basket when it has three souls sitting in it to send it away.
4) Keep clicking animal souls while your basket is away, they will follow you and three of them will jump in the basket when it returns.
5) the basket takes like 15 seconds to return to you per the debuff.
This quest seems needlessly complicated but rather simple once you know the animals will follow you. It just takes time as you can only send three animals at a time and it takes 15-20 seconds for your basket to return and the souls to jump inside it.

Go to the river look for Druid souls, aka bunnies, corgis dogs, rabbits.. Click them. wait for the basket to be full, send the basket back. do that 4 times.

Despite what the tooltip for [spell=353575] says, you can send three souls at a time, and the rest will stick with you until it comes back, at which point the next three will automatically hop on for the ride back to Thiernax!