What happens with multiple copies of Humility and Glorious Anthem on the battlefield?
Humility sets the base power and toughness to 1/1 for all creatures. Glorious Anthem, and other effects like +1/+1 counters are still applied on top of the base power and toughness, so (barring other effects), with one or more Humilities and two Glorious Anthems on the battlefield, your creatures will be 3/3s.
The relevant rule is 613:

613.3. Within layer 7, apply effects in a series of sublayers in the order described below. Within each sublayer, apply effects in timestamp order. (See rule 613.6.) Note that dependency may alter the order in which effects are applied within a sublayer. (See rule 613.7.)
613.3a Layer 7a: Effects from characteristic-defining abilities that define power and/or toughness are applied. See rule 604.3.
613.3b Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.
613.3c Layer 7c: Effects that modify power and/or toughness (but don't set power and/or toughness to a specific number or value) are applied.
613.3d Layer 7d: Power and/or toughness changes from counters are applied. See rule 121, &quot;Counters.&quot;
613.3e Layer 7e: Effects that switch a creature's power and toughness are applied. Such effects take the value of power and apply it to the creature's toughness, and take the value of toughness and apply it to the creature's power.

Layer 7a is the creature's power and toughness as it's printed on the card, say a 2/2 Grizzly Bears.
Layer 7b (note the use of &quot;base power and toughness&quot; in the rules) is where Humility comes into play, it makes it a 1/1.
Layer 7c is Glorious Anthem's layer, if you have two of them both apply and the 1/1 becomes a 3/3.