Can two roomates both claim head of household for taxes?

No. To calim H-o-H you must provide at least half the cost of upkeep of the home. Obviously two people living in the same home can't each claim to have provided more than half the upkeep of that home. Also, you don't mention the situation regarding dependents - I assume you realize that H-o-H can only be claimed if there are dependents involved, so besides these two roomates are there also dependent children, spouses, parents, etc involved?