Q.Help with my lavender hedge
I am totally new to gardening. I live in the East Bay of the San Francisco Bay Area, so we get a very warm fall. A couple months ago, I planted several Hidcote Lavender plants (and my husband accidentally planted a couple that were a different kind of lavender). We want to grow a hedge, which is why they’re closer together.
TWO QUESTIONS:
1. Are these other sprouts/seedlings lavender, or are they weeds?
2. Is it time to harvest/prune the more mature plants?

The plant in the image does not appear to be Lavender of any variety that I know of.
The rounded leaf and even the growth appear to be Oregano to me, but this could be many other types of plants also.
Difficult to say 100 % what the plant is. Crushing the leaves and seeing if the plant has an aroma can help identify it.
You can began pruning your Lavender plants when they have been in the ground for 1 year.
Here is a link that will help you.
https://www.gardeningknowhow.com/edible/herbs/lavender/pruning-lavender.htm