We'll be needing a layout with dimensions, with windows and doors marked it. And photos.

Help others help you by posting an overhead view layout, drawn to scale on graph paper with all dimensions (walls, windows, doors, etc.) clearly marked. Be sure to show all the rooms so we know how they connect. Then tell us what you want to place in there (sizes/types of furniture, etc.) And just curious, are those concrete stairs and how are they supported?

Congratulations on the new house! In terms of what to put in this space, I do like the dark couches and how they contrast with your light walls and carpet. You do need some color, though. Some wall art that's high up enough where the kids can't play with it would help. Oranges and reds would brighten the room a bit and bring some visual interest. A coffee table to unify the couches a bit more could also help warm the space. I'm always a huge fan of natural woods with a smooth finish, like you can see here. You could probably get some bumpers for the corners of the coffee table so the kids didn't poke themselves by accident.

You can probably add another chair. Some C-tables and/or nesting tables could be useful. https://www.amazon.com/Rivet-Mid-Century-Nesting-Metal-Walnut/dp/B07B7ND7YH?ref_=mh_s9_apbd_omg_bFfRN&pf_rd_r=6TW0VSGHAV2GDVJ0TM8W&pf_rd_p=28245ff4-a514-5609-85c1-0cca6e15f7c7&pf_rd_s=mobile-hybrid-11&pf_rd_t=BROWSE_ANYWHERE&pf_rd_i=3734221 https://www.amazon.com/gp/aw/d/B07ZHG9318/ref=mp_s_a_1_6?ie=UTF8&qid=1591278648&sr=1-6&pi=AC_SX236_SY340_QL65&dpPl=1&dpID=71p5WdXZ-ZL&ref=plSrch&th=1&psc=1 https://www.wayfair.com/furniture/pdp/williston-forge-oakhaven-end-table-w000250868.html