Looking for advice: uniting grocery shopping lists

Greetings excellent people!

I used to be a bit more proficient in Excel, nowadays I can use functions but have a little bit of a hard time getting where I want.

Case is this: (sorry if some words aren't PC, I'm not a native speaker)

I work in a residence where differently challenged and challenging people live and are assisted in their daily lives.

I want to create an Excel file where different people write their shopping lists (grocery) and those (like 5) lists are brought together and added up into one list.

Now, with a set list of given groceries where people just add in numbers (like eggs: ..., apples: ....,) I do not have a problem.

What I want is for people to be able to add their own items, that are then added to the summary list (bonus if similar items are put together).

I am already trying stuff and will possibly get back here when I have more specific questions; at this time I'd like to ask for general advice or tips that come to your mind if you hear what I'm trying to do.