Extracting Unique data based on case id without UNIQUE

Hello. I am trying to automate a report that my coworkers have been filling out manually for 15 years. I am able to generate a html report from our web-based database which gets imported into excel, tweaked, and spat out to Word by way of Mail merge.

I made a super simplified version of what the data looks like in excel. Cases will show up on multiple rows if there are more than one of some the data points that I am pulling (for example, multiple pets or multiple visits). (There is nothing I can do about this. It is how reports are generated.) I need a way to check the range of cases with the same ID and extract a unique list of pet names for each case. This will then be called for in extra columns till all the unique information for a case is on 1 row.

I know UNIQUE and FILTER have this capacity, but I don't think they will work for my situation. I have one sheet that the raw data goes into, and another that tweaks it for Mail merge (marking first instance, turning "5 years" into "5", etc.). I need each cell in the "2nd pet" and "3rd pet" columns to have formulas so that no matter what data I drop into the raw data sheet, it can generate a list. As it stands, UNIQUE seems to require a truly empty cell under it. I was hoping and IF function with "" outputs would work, but they did not.

I'm happy to correct to a simpler path if I've taken a wrong turn somewhere. I hold the distinction of being the most computer literate person in the office, but I am far from being an expert.

All names and information are fictional.