Now things are starting to come full circle, as the Huthis are allegeding that the Yemeni government is using al-Qaeda fighters against their own fighters in and around Sa'dah. This comes just as the Yemeni government is claiming that it has arrested five Iranians on a boat with weapons that were destined for the Huthis.
So if one believes the Yemeni government then the Huthis are allied with: al-Qaeda, Iran, Hezbullah, Shi'a in Bahrain and throughout the Middle East who are supporting their co-coreligionists in Yemen as well as Iraqi Shi'a in the Iraqi government.
If one believes the Huthis then the Yemeni government is allied with: al-Qaeda, Saudi Arabia, former Iraqi officers loyal to Saddam Hussein (who are allegedly flying bombing raids) and the US.
(Various other smaller actors have allegedly played a role on both sides - but the ones above are the main ones.)