Garnet: "heh... I know."
Of course she knew, she had to have a little peek into the future to ensure your stay there would be beneficial.
But that didn't keep her from being excited. Not only did your love withstand the grips of corruption, but now she was going to see it in its purest form; the long lost gemling.
Ameythyst: "Aw, really!? Haha! Yeah!"
She isn't too familiar with gemlings since she's never been to homeworld, but after an explanation from garnet, she was more than thrilled to be having more little gemmys roaming around.
Pearl: "SHE'S WHAT!!?"
Pearl could've easily poofed from the sheer amount of surprise the news brought her. Heck, her gem might as well crack from the shock... and maybe excitement from the thought of seeing another gemling...
N-Nevertheless, it was bad enough that you both had corruption, but for gemlings to come into such a state? That cure can't come quick enough! Let's just hope they're well behaved until then...
Steven: *GAAAAAAAAAAASP!*
HE'S GONNA BE A BIG BROTHER!
...that's all he could think of in that moment.