As far as I know, there isn’t an easy way to make subgroupings within projects, though I’ll be interested to learn how to do it if there is.
If the observations you’re working with are yours, you could add a tag (like “invasives from my yard”) to the observations you want to group, do a search for those tags, save the web address of the search output, and paste it into a journal entry in your project (like, To see all the invasives, click here). As an example, I did something similar for one of my projects to show off all the cool species that visit my butterfly feeders: https://www.inaturalist.org/projects/my-kentucky-yard/journal/68071-finds-from-the-rinds
You can’t add tags to other people’s observations, but you can usually add observation fields, and I bet there’s already one made for invasive species, so you might also be able to mark observations that way, search for them, an then use a similar approach as I outlined above.
An umbrella project where you collect subprojects (like Natives of My Yard + Invasives of My Yard) could also work, but would require building several projects.
One option: From the web site, use the Explore tab atop the page, and enter the location of your project or find it in map view. This will give a list of observers and identifiers in that area. You can enter a species to refine who has made the most observation and IDs in that place (leaderboards). This isn’t a list of scientists.
I recently started using tags where I wanted to show lists of all of the butterflies that I was observing on my blackberry blossoms. I have now made several other such “lists” using tags. I preface my tags with three letters that represent the property I am involved with, to minimize the risk of someone else using the same tag.
Yes, it is. Anyone who observes or identifies organisms is engaged in science, and is thus a scientist.
In these modern times, even some academics will acknowledge the contributions of those without equal stature (just joking, I suspect that by now it may be a majority of academics, not just some).