do both creatures need soulbond for it to work?

[SHAY]

do both creatures need to have soulbond for it to work?

[Kenji]

Not at all. If only one of the paired creatures has soulbond, that's just fine. I'd rather not quote a huge block of text, so just check out the Avacyn Restored FAQ on your own: Avacyn Restored Frequently Asked Questions : Daily MTG : Magic: The Gathering

You'll find under the entries for Soulbond that it mentions nothing about needing both paired creatures to have soulbond -- that would be a pretty important thing to point out, were that the case. But it's not, which is why there's nothing written about that.

Of course, also note that two creatures with soulbond can be paired with one another, if you so choose.