There should be more than two Biomass altars... I'm aware of four on my world and there's probably 1-2 more.

For the other problem, you'll want an iron mace and a good parrying shield. Iron buckler and maybe even banded shield, fully upgraded, should be able to parry and stagger them.

If you don't wish to create another iron tier weapon, you can go for Frostner. Best value weapon in the game right now... though, if you have max upgraded iron sword, it may not actually matter which you use. Either way, silver shield should be able to parry them from the get-go without any upgrades, at least with average blocking skill...

And you'll obviously need good food so you don't get staggered yourself and destroy your parry. Golems deal 110 pierce or blunt damage depending on their arms.