explaining Sam and Tara
Honestly, I think the best way would be tongue-in cheek. After Sidney and Gale reunite, Gale can say she called Sam and Tara.
Sidney: "They're not coming here, are they?"
Gale: "No, they're hiding in a safe place. They deserve their happy ending."
And leave it at that.
If they over-explain, they risk painting themselves into a corner for future installments, should Sam and Tara return. Or, to that, don't explain/mention them at all. Goes along with the whole recent "ignore all sequels and pretend this is the first direct sequel to the original" trope