If I had an egg which was taking ages and ages to hatch I could use a Pokemon with flame body, but would it be any faster if I had two Pokemon in my party with flame body?
Also if you have time please tell me if flame body is better at hatching eggs than magma armor and please give me an example of a Pokemon with magma armor.
The effects will not stack. No matter how many Flame Body Pokemon you have in the party, only one will have effect.
Also, Flame Body is not better than Magma Armor or vice versa.