Working for a customer fixing hurricane damage and this is first time installing product. Looking for some advice on how to navigate this situation.

The height for cut was right in line with where railing attaches. The panels dont appear to work next to stairs because I can’t get behind to install base-klips or baseboard to hold it in place. Also there is an outside corner to deal with where it meets stairs on other side. Rest of house was “easier” once I learned the product but this section has me stumped. Any thoughts?