I'm hanging new drywall and took down the old drywall today. I noticed that two studs were pretty loose. I'm not exactly sure how to reattach them to the wall. Right now, they are nailed into a brick wall which is the adjoining wall with another house. Any help is appreciated, thanks.

Are they 2x4 studs or furring strips? Probably furring strips (1x2, 1x3, 1x4) boards nailed to brick. Nail to brick with cut nails and big hammer.

Agree but make sure you nail into a mortar joint not the actual brick unless they are actually concrete blocks.

Not sure what type of brick it is but they are definitely furring strips. Where the nails are in the other studs, there are also small strips of wood between the wall and the stud. I saved the ones that fell out so I will place them back in before I nail. Thanks.

Just shims to keep furring strips straight.