On Rosh Chodesh and Chol Hamoed we read the torah with 4 different people, no more and no less, and there is not haftora.

On Yom Tov we read with 5 people.

On Yom Kipper we read with 6 people.

On Shabbos we read with 7 people.

On all these you cannot read with less people. On Shabbos you can add to how many people read.

Megila 4:3

Pores al shema means that after people finished davening without a minyan they got together to say kaddish and kedusha and the first bracha of Shema.

You need ten male adults for the following; to be Pores al shema, to say chazaras hashatz [repeating of the shmone esrei], to have the cohanim give their blessing, to read the torah and haftora, to maamad umoshav [to stop and sit with the deceased as you go to the burial], to make the brachos of an aveil or tanchumin, to make the brachos of a choson, to make a zimun by benshing with Hashems name. For redeeming a land from kodesh or figuring out a person’s worth (i.e. someone said, ‘the worth of this person is upon me’), you need nine people plus one cohein.