Drapes will help solve this. The more fabric etc you have the better it is for you that. Have you fully furnished your upper landing/loft? We have a similar issue and every time we add a rug as we work on the home we’re finding the echo is improving a lot.

Elimination of hard surfaces may do the trick. Added sound absorption such as lined drapes, wall hung tapestries or sound dampened fabrics, large plush area rugs, fabric seating pieces rather than leather, lots of soft pillows. Looking below, I think I'd start with draperies at your windows and a fabric or tapestry hung above that big opening. Both upstairs and down you could do a foam core upholstered wall like the second photo below. All these are easier than closing the upstairs off.

Big area rugs will help that

You need heavy pads, thick heavy carpets, lined draperies, and padded, upholstered furniture to absorb sound. Thin, fluffy cotton won't work.