The Component Substitutions Sidebar on page 303 of the CRB2e says that...
"If you’re a sorcerer Casting a Spell from the magical tradition that matches your bloodline, you can draw on the magic within your blood to replace any material component with a somatic component."
If you are casting a spell with both material and somatic components, such as black tentacles, would you be unable to cast the spell, would the somatic components combine into a single action, or would you have two somatic actions for the spell?