First I want to point at the fact that your 2nd hadith is only qualified as da'if because of the weakness of the narrator Abdullah ibn Kharaash عبد الله بن خراش (who has even been called a liar) and with the addition "...and their price is unlawful." (by al-Albani for example) as you may find it in other hadith collections like Musnad Ahmad and sunan abi Dawod where it is qualified as sahih without this extension and without Abdullah ibn Kharaash in the narrator chain.
Note that in the Arabic text there's a comment of this Abu Said (the one from whom ibn Majah has narrated the hadith directly, so he is one of his teachers) right after the statement of the hadith saying that this is to be understood in the context of running water.
Note that the teacher of ibn Majah Muhammad ibn Abudllah ibn Yazid abu Yahya al-Makky محمد بن عبد الله بن يزيد أبا يحيى المكي (on whom's authority ibn majah has narrated the first hadith) the narrator of the chain of the first hadith, as he has been qualified as trustworthy by an-Nasa'i and ibn abi Hatim, and others while the rest are narrators of the two sahihs.
On water and pasture
In general you can group them into three classes:
- Shared water like the water of the sea, rivers etc. these should be accessible to everybody and all people can share it as it is a public property.
- What a private person owns like a tank or reservoir or jar etc. so this is private ownership and should only be taken from with the owners permission.
- A well on a land which somebody has bought or something he worked for for example he has carried water from a river or lake etc. for these there is theological dispute on whether the person needs to share it or he is allowed to deny it. A related hadith is in sahih al-Bukhari.
Explanation of the ahadith
As the order in sunan ibn Majah is reverse to your Post I'll start with the order in sunan ibn Majah as of course teh commentary on the first hadith -in the correct order- would be longer than for the second!
Hadith 2: in his commentary on sunan ibn Majah as-Sindi said that some peolple have taken the hadith as is interpreting it that these three things are not allowed to be in private ownership nor being declared for sale at all. But the most prominent between the scholars is that the posture meant here is that one on a land that has no specific owner, while the water meant is the water that comes from the sky (rain, snow etc.), rivers and natural springs which can't be in private ownership, while fire refers to wood and dead wood of trees that people heel to use it for their fireplaces. So for the water if somebody got some and put it in a vessel he would be allowed to sell it and the same applies for the other two. Al-Khatab الخطابي in his comment on sunan abi Dawod has said: posture here is what ever grows in a land that doesn't belong to anybody, where people just collect or yield it (freely), nobody could or is allowed to hinder others from using it. The fire was explained by life coal so nobody has the right to hinder others from taking the pebbles, some said it is allowed to hinder people to take pebble but not from coming close to the fireplace to get warm or to light up a lantern as this doesn't change the fire itself.
Hadith 1: In his commentary on sunan ibn Majah as-Sindi just said that these things (he emphasized on fire and water) shouldn't be forbidden to people who are in need of them and the neighbors.
This means if you are in need of this water (for example) you are not ordered to share it, but if you have something left and your neighbor is in need or somebody knocks on your door asking for water (maybe to drink) you should share it!
So most scholars are in consensus about posture or water which is in a desert or a wide land: nobody is allowed to hinder others from (using) it. While private ownership has other rules.