The kingdom building system is based around the concept of "build points"; a set amount of resources which abstractly encompasses a variety of elements such as raw materials (milled lumber, bricks and worked metals), settlers, contracted specialists (engineers, clerks, craftsmen, etc), physical labor, political alliances and in some cases straight cash-money. They can be gained from a variety of means, most often through collecting taxes and tithes, and are spent in maintaining the upkeep of a kingdom or to create/develop new holdings. As a reference point, a single BP can generally be acquired in exchange for 4,000 gp worth of treasure or commodities and, in turn, a BP can be "sold" for 2,000 gp in cash.
Although our Rostlandir heroes currently have some raw materials, laborers and allies at their disposal, it only amounts to perhaps 2-3 BPs in total; enough to build a meagre settlement with a handful of buildings and families while leaving them relatively destitute. If they want to create a thriving settlement in less than a few decades they'll need to acquire additional BPs as venture capital.
The Rostlandir's primary sponsors thus far are the Aldori Swordlords and Restov's Lord Mayor's office. With a vested interest in fortifying Brevoy's southern border, both can be expected to help shoulder the burden finance the establishment of a new settlement and to recruit colonists. The Rostlandir might want to consider going further by soliciting aid from other groups within Brevoy or beyond to increase their initial pool of resources. As might be expected, those groups might have their own interests in the venture with corresponding demands in exchange for their aid however.
There are only three or four churches with holdings in Brevoy substantial enough to offer any significant aid in founding a settlement:
Abadar. The Master of the First Vault is the unifying religious power in Brevoy, favored of the merchant and tradesman class, as well as those nobles more interested in prosperity through trade and the rule of law than the iron fist of battle. With its vast reserves of wealth, trade connections and familiarity with establishing fair and efficient bureaucracies, the church of Abadar could prove a powerful ally for a fledgling colony.
Gorum. Our Lord in Iron speaks to the needs and interests of the nobility of Brevoy: strength through force of arms and prowess in battle. Although his church's monetary resources are substantial, it's likely the ease with which the faithful could fill the ranks of a would-be-ruler's civil and foreign armed forces that is most attractive to a fledgling ruler.
Pharasma. Our Lady of Gentle Repose is the divinity of the common people of Brevoy, who are generally more concerned with cultivation, birthing, harvesting and the afterlife than wealth. The church's influence and ability to mobilize its sizable congregations of farmers, herders, fisherfolk and craftsmen could greatly ease the burden of recruiting colonists.
Erastil. Although Old Deadeye's church is a minor one and hasn't the holdings or monetary resources of Brevoy's three primary faiths, worship of Erastil is not uncommon in far-flung rural areas. Their primary resource may be good-hearted and robust homesteaders eager to settle new lands.
Modern Brevoy was formed by the forced joining of two culturally distinct areas over three hundred years ago by Choral the Conqueror: Isia in the north and Rostland in the south. Although there are dozens of minor noble houses, only the six largest remaining houses (the seventh ruling house mysteriously disappeared over ten years ago) have the clout and wealth to offer you any significant aid in settling a new region. Although, being Rostlanders, your inclination might be to stick with other Rostland noble houses, all are included here for consideration.
Rostland noble houses
House Medvyed. Sharing some ties of blood with Isia, this house of herders and hunters in Brevoy's eastern reaches are known as rustics with a known devotion to Erastil. Lord Gurev Medvyed loves to hunt, ride, and feast with his men, and dotes on his wife and children. The house may welcome the opportunity to establish new pastures and hunting grounds in the south.
House Lebeda. The most traditionally Rostlandic house remaining, the Lebedas earn and maintain their fortune as merchants and brokers between the northern and southern reaches of Brevoy, and control much of the shipping across the lake of Mists. Dame Sarrona Lebeda has ruled the house as regent since the death of her husband on behalf of their young son Lander. Rumors claim the Lebedas are looking to arrange a marriage between his older sister Elanna and Noleski Surtova. They might welcome the opportunity to establish a new trade route so as to expand their influence southwards.
Isia noble houses
House Surtova. The most influential of Brevoy's noble houses, the Survotas established a “regency” in the absence of King Urzen Rogarvia, which has recently been proclaimed as the new monarchy by King Noleski Surtova. This ascendancy to the throne remains contentious and divisive. Regardless, the house is seeking to establish a stronger presence in Rostland and may welcome the opportunity to invest in your venture.
House Orlovsky. From Eagle's Watch on the slopes of Mt. Veshka, House Orlovsky seeks to remain above the conflicts in Brevoy, both figuratively and literally. Unfortunately, the house's role as a staunch ally of the Rogarvias (the missing house) has placed it in an awkward position under the current regime. They might welcome the opportunity to establish some holdings in the south if only to keep House Surtova from doing the same.
House Lodovka. Proudly Isian, house Lodovka's fortune is tied to maritime mercantilism upon the Lake of Mists. They might welcome the opportunity to expand their seafaring trade into the River Kingdoms via Tuskwater lake and could likely help establish a port there.
House Garess. The valleys and lowlands of the Golushkin Mountains are the domain of House Garess, founded on both the defensibility of the mountain terrain and the mineral wealth the house has brought out of the peaks for generations. If there's mineral wealth in the Stolen Lands, House Garess would likely be willing to help establish mining operations there.
And there are of course a variety of wealthy commerce groups, agricultural co-ops, merchant guilds and consortiums in Brevoy that might be willing to invest in your venture for the sake of profit. They could help build infrastructure, swell communities with the families of their laborers and boost your economy in exchange for the rights to extract various natural resources from this largely untouched frontier for the sake of future profits.