So have you tried the multi-assign stuff from the article? I’ll do an example here because what you’ve said makes me feel like it should work for you. My team’s not very big and we don’t tend to have duplicated tasks too often, but when we do it’s nice.
Basically you start with a task, whether a new one or one that’s been copied. Once you have the task that you want everyone on your team to work on, you click in the assignment field and then the icon of the two people in the right-hand side of the field:
Then you type in your team’s name:
It’ll confirm how many people will get it:
This’ll happen:
And you end up with this:
I’m never sure why the one empty one remains, but I typically just delete it.
Now I need to go get rid of all these tests before my team notices 
You can also type in individual people if you don’t want the full team, but even that still saves a ton of time.
Hope that helps, if not, more details of what isn’t working might help me come up with something else.