Yes, hibiscus can be divided, and now, or within the next few weeks, is a good time. Dig it up, and if possible try to separate them into several plants. If that does not work, cut off the roots that link the plants to be separated, but make sure each segment has plenty of roots. Then give the plants choice topsoil in their new locations which should be spacious holes. Water thoroughly and keep the soil moist to touch for about ten days.
Pampas grass is wonderful but it is marginal in our area.
You are lucky if it survived this winter. It is not unusual for an ornamental grass not to develop plumes in its first year in a new location. Cut off the dead stalks now and put some cow manure, or better yet, goat manure all around the plant. If it is in the shade, that might be the reason it did not have plumes. I'd transplant it now in that case.