Microsoft Excel: Places a list of cell data in a single cell based on specific values

I know the title of the question is not great, I can not think of a good way to formulate the question, which makes it difficult to find answers by simply searching online. I do not have much experience in Excel, but I am usually able to understand how to do something with some quick google searches.

Until now, I have tried several combinations of functions TEXTJOIN (), FILTER (), SEARCH (), and FIND ().

I'm trying to make a schedule based on free time.

I've used Google forms to poll people every day they're free (sheet 1).

Sheet 1 (Data)
A B C
NAME MON DAY
1 Dan 1, 2, 5 1, 4
2 Robert 12, 3 12, 3
3 Gregg 1, 2 4,
4 Joe 2, 3 3,

I want to be able to see the overlap of free time so that I can create a schedule when two people are free at the same time.

Sheet 2 (Results)
A B C
1 hour Monday
2 12 Robert Robert
3 1 Dan, Gregg Dan
4 2 Dan, Gregg, Joe
5 3 Robert, Joe Robert, Joe
6 Dan, Gregg
7 5 Dan