Hmm...then:
[X] Plan Bend Thy Knee
[X] Accept the deal. Instead of raiding Brushcrest, the Valley People will march with them against the People of Makar.
-[X] Brushcrest will bend the knee and become a tributary of the Valley Peoples. A tributary payment will be sent every turn from Brushcrest to the Valley, with exact terms to be negotiated later. In return their chieftain and council will gain the right to represent themselves before the Council of Three, but not a voice in the succession, and the other rights expected will be withheld. Though, should Brushcrest ever become a village of the Valley Peoples, said rights will be accorded.
-[X] Brushcrest will give up the right to make major deals (alliances, etc) with foreign powers without Council approval, though smaller things like trade deals are fine.
-[X] Brushcrest will allow the Speaker and Bone tenders to preach freely in Brushcrest, and will see to it that no harm will come to them.
-[X] Brushcrest will be allowed to maintain its faith but Water Maidens and that water faith will not be allowed to preach outside Brushcrest and its outlying villages. Attempting to preach to the Valley People, White Clans, or other parties without the express permission of the Bone-Tenders and Council of Three will be considered an act of violation, and punishable by execution of both the offender and close family.
-[X] Members of the water faith will not be allowed to settle in the Valley or amongst the White Clans.
-[X] In return Brushcrest will be under the protection of the Valley People, and the Valley People will see to it that they are not destroyed.
going full Serbian Ultimatum I see
-[X] Brushcrest will bend the knee and become a tributary of the Valley Peoples. A tributary payment will be sent every turn from Brushcrest to the Valley, with exact terms to be negotiated later. In return their chieftain and council will gain the right to represent themselves before the Council of Three, but not a voice in the succession, and the other rights expected will be withheld. Though, should Brushcrest ever become a village of the Valley Peoples, said rights will be accorded.
Acceptable.
-[X] Brushcrest will give up the right to make major deals (alliances, etc) with foreign powers without Council approval, though smaller things like trade deals are fine.
They might accept this, but probably not. They are a trading and diplomatic power, after all.
-[X] Brushcrest will allow the Speaker and Bone tenders to preach freely in Brushcrest, and will see to it that no harm will come to them.
Acceptable.
-[X] Brushcrest will be allowed to maintain its faith but Water Maidens and that water faith will not be allowed to preach outside Brushcrest and its outlying villages. Attempting to preach to the Valley People, White Clans, or other parties without the express permission of the Bone-Tenders and Council of Three will be considered an act of violation, and punishable by execution of both the offender and close family.
Whoaaaaa. There is no way in hell they would accept this. Execution of both the offender and close family? You really are going full Serbian situation here.
-[X] Members of the water faith will not be allowed to settle in the Valley or amongst the White Clans.
Acceptable.
-[X] In return Brushcrest will be under the protection of the Valley People, and the Valley People will see to it that they are not destroyed.
Duh.
[X] Plan Jolly Cooperation
[X] Accept the deal. Instead of raiding Brushcrest, the Valley People will march with them against the people of Makar.
-[X] Brushcrest will bend the knee and become a tributary of the Valley Peoples. A tributary payment will be sent every turn from Brushcrest to the Valley, with exact terms to be negotiated later. In return their chieftain and council will gain the right to represent themselves before the Council of Three, but not a voice in the succession, and the other rights expected will be withheld. Though, should Brushcrest ever become a village of the Valley Peoples, said rights will be accorded.
-[X] Brushcrest will give up the right to make alliances, declare war or raid other powers without Council approval, but smaller things are fine. Current alliances will be respected unless broken.
-[X] Brushcrest will allow the Speaker and Bone tenders to preach freely in Brushcrest, and will see to it that no harm will come to them.
-[X] The Water Maidens will not be allowed to preach in Greenvalley or to the Clans. They may send expeditions up the Gentle River, but they must not set foot on Greenvalley soil under penalty of summary execution. They may, however, request help from river dwellers if necessary.
-[X] Members of the water faith will not be allowed to settle in the Valley or amongst the Clans.
-[X] Brushcrest will not build north into the lands of the Valley People, or attempt to block passage down the river. They may expand east or west or try to cross the seas, if they wish.
-[X] In return Brushcrest will be under the protection of the Valley People, and the Valley People will see to it that they are not destroyed.
-[X] Explain that they are asking us to turn from an enemy to an ally on basically nothing but their word. Tribute might seem a steep cost, but the benefits will be worth it; no more raiding from all sides, destroying their every effort. Without raiding taking its toll, they should easily be able to pay tribute and continue to grow. A few shells is a cheap price for safety.
I edited it a bit so we're not completely taking their sovereignty, just the bits they don't care about. We can easily find an excuse to break their alliance network whenever we want. You really want an excuse to keep raiding these guys, but I'd much rather go after the river raiders to be honest. By making Brushcrest a tributary and defeating the main threat in the area, we'll make ourselves regional hegemon. We can continue to spread with soft power and look for shiny rocks in the mountains. Turning inward for a little bit might be good honestly.
Also, I want to see what kind of loopholes the Maidens come up with. Eventually we're gonna get a short story with someone carrying a Maiden through Greenvalley on their shoulders because their boat capsized. It won't be enough to actually preach or anything. Executing their whole families is pointlessly harsh. Not "exerting our power" harsh, just "making martyrs and looking dumb" harsh.
edit: added no raiding, they won't care but don't want these dumbos starting a war unless we want it