Marvels Comics Group shows up as 1 series with eight issues, but they all are marked as number one, most of them without a variant marker. It also looks like all of them have the description of the FF issue, but I think all the politics are unique.
I just found the X-Men one. The indicia label it as Marvels Comics: X-Men #1, Vol. 1, No. 1, July, 2000.
Here’s a description of the event: https://earthsmightiestblog.com/marvels-comics-group-one-shots-2000/
My recommendation would be Marvels Comics Group: X-Men #1. Marvels Comics Group: Captain America #1. Etc. All listed as separate series, even though they are part of the same event, based on the tradition of The Marvels series.