Hi Fernando,
Wished i could say something in portugese to you. Your dutch is better than my portugese
Those lances are very nice indeed. Certainly the first two ones, about the third one i'm a bit unsure. The haft is similar to your piece but mine has an uncommon spearhead. Don't know what to think about it.
I think you're right about the rattan material. The peeled bark is weaving material and what remains can be used for a shaft.
You got yourself a very nice and aged sumatran lance. Congrats with this one, it certainly deserves a place in your collection.