On your grandchild's what? Be specific to get specific answers. Anyways that would be:
'Mago-san no koto omedetou gozaimasu'.
You may say 'omedetou.'
omedetou
Felicitaciones por su compromiso.
we say Nakagawa if we want to say inside in Japanese.
メロン is how you say melon in Japanese.
You may say 'omedetou.'
第八孫 this is a way to say eighth grandchild in Japanese. If you have any more questions on translations I recommend trying translators such as Google translate or babel fish.
congratulations on.
No, you cannot say, they send their congratulations. You have to say they sent their congratulations.
omedetou
congratulations
"Proficiat" is how you say congratulations in Flemish.
no flowers say congratulations
娘 (musume) is daughter and 孫 (mago) is grandchild, so 孫娘 (magomusume) is granddaughter.
In Filipino, you would say "Congratulations" as "Congratulations" or "Pakaka-bait."
You can say "čestitke" in Bosnian to say congratulations.
In Hindi, you can say congratulations by saying "बधाई हो" (Badhai ho).