I just finished translating these as best I could. There are still some meter problems for English singers in my translation, but that's a minor matter to correct and tweak.

I've provided the original Japanese lyrics with my translation here. What do you think? Please, be brutal - I want this to be the best I can make it.

Original:

かぞえきれない　きょうだいたちと
あぶくのことばで　はなしていたの

おぼえていますか　ずっと昔に
お前は青いうみに　いっしょにくらしていたの

クラゲもウニも　サカナもカニも
みんな　きょうだいだっ
おぼえていますか　ずっと昔に
お前は青いうみに　いっしょにくらしていたの

海ゆりゆれる　青いうち
おぼえていますか　きょうだいたちを


My translation:

Seaweed waving free in the deep blue sea.
You''re part of a great family, together with countless siblings,
You speak to us in the language of bubbles.

Don't you remember when we swam together?
It was such a long time ago.
We were together in the same waters; parting was the hardest thing we've ever done.

Jellyfish and sea urchin, countless fish and crabs,
We are all a living family!

Don't you remember when we swam together?
It was such a long time ago.
We were together in the same waters; parting was the hardest thing we've ever done.

Seaweed waving free in the deep blue sea.
We are all a living family!