#fumigate

You won’t get any triggers at all since Firesong and Sunspeaker die to Fumigate before you gain any life.

However, if Firesong and Sunspeaker has Indestructible or is regenerated or otherwise somehow not destroyed by Fumigate, then its second ability will only trigger once. “You gain N life for each [something]” effects are a single instance of lifegain, not multiple instances.

Yes.

When resolving a spell or ability, you follow its instructions in the order they’re printed. For Fumigate this means that you first destroy all creatures and then gain life. Rampaging Ferocidon is no longer on the battlefield when you would gain life, so there’s nothing stopping you from gaining that life anymore.

Fumigate

Artist: Svetlin Velinov Set: Kaladesh

Fumigate

"Ghirapur's gremlin population poses a threat to the infrastructure of the fairgrounds. Threats must be eliminated." —Sram, senior edificer