Emerald Green arborvitae will never get to be 5-10' wide........perhaps 4' at the most but 3' is the most standard width for these, even after many years. Other than their height, which could become a bit intimidating that close to a side walk or road (not to mention block any necessary lines of sight), I see no reason to remove them. And even that can be controlled by pruning and/or shearing into a more hedged appearance. They would not have been my first choice but not my garden :-)

I'd just pick whatever evergreen groundcover is available in your area that will grow under the conditions provided. Nothing tall and nothing fancy. In that location you want durability and low maintenance.

I was told they grow 2-3'w. I also plan on trimming them if they get too big.

Not all propagations of 'Smaragd' produce the same exact shape on every planting site, some can end up developing a pretty broad base relative to their height. Might involve positions on stock plants of cuttings used, might be a varying response to individual site conditions or it might be both. But it remains that examples a full 3 ft. wide are going to be quite some years in the making. At which point it probably would in fact be their associated height that might become seen as unsuitable for the situation asked about here.

Thanks for the response. At this point, what would be my best option?

Leave 'em. They are already bought and planted so just a waste to dig them up and toss them. And if you are prepared to do so, you can keep them trimmed to the height and width you want. Relatively easy to maintain as a hedge at the height you want as long as you start the process early enough and your diligent with the maintenance. IOW, don't wait 2 years before pruning :-)

Thanks. Do you think I should put rocks behind, mulch or grass behind the trees and the driveway (about 2')?

I can't tell what's driveway, what's walkway or what's road :-) Do you mean the area circled in blue?

Yes the circled blue.

Not rocks, mulch or grass.....groundcover.

Any suggestions? I'm in zone 7

If you want to plant now go see what is being presented at outlets there and choose from among those. No point in having somebody here recommend something specific only to discover you can't find it there. Or what you find of it is not appealing. Apart from this being the case at all times in addition during the pandemic a new combination that has arisen is feeding frenzies* at plant outlets due to homeowners staying put and working on property improvements - at the same time that plant producers have limited access to labor. With the result that it has been predicted that the market ready nursery stock supply is going to dry up completely later this year.

*A longtime independent garden center employee characterized the situation to me as "Where they used to grab one or two pots now it's the entire flat"

I would pull out the grass and mulch that entire area. You won't be able to mow or trim once they grow much more. You can plant some smaller perennials between the trees and sidewalk for now until they grow.