Putting a token creature with devour onto the battlefield works the same as putting any other creature with devour onto the battlefield. The token may devour Dragon Broodmother itself!

In a Two-Headed Giant game, Dragon Broodmother’s second ability triggers only once at the beginning of each team’s upkeep, not once for each player. You’ll get one Dragon token at the beginning of your team’s upkeep and one Dragon token at the beginning of the opposing team’s upkeep.