Hachinan tte, Sore wa Nai Deshou!

Some things to note:

 

Keep in mind the nobility system, as there's only two ways to gain peerage. Either being hereditary or by performing some kind of achievement.

Wend, for killing the ancient dragon, rose to an appropriate Rank 6 Associate-Baron. Most likely this is considering the outstanding achievement and that he comes from a Rank 7 Knight family. And in recognition is allowed to start his own "household', which is also called Baumeister. This gets confusing in the novel because you have to make the distinction between Baumeister (Country side family), Baumeister (Wend's new household), and the Baumeister (Capital-side family). They're all seperate households but the last one has yet to be introduced in the manga but remember how Wend's ancestor was the second son of a knight household in the capital, that's the branch from the oldest son that remained in the capital. 

 

Basically Wend's family which I will refer as Baumeister (Country-side hick) is a rank 7 knight household. The Knight title gets passed down from through the family heir's which in this case is the oldest son, Kurt. Originally Wend's Great-Great-Grandfather was the second son of a knight. He basically inherited nothing and couldn't make a place for himself in the capital. He had no pre-planned future (like our current wend's other brothers). and decided to go pioneer a new land in the wilderness. As a rare exception, in recognition of starting a new territory in a difficult place that no one wants to, Wend's ancestor was given the title of Rank 7 Knight and the rights to develop the land. Thus how we have the Baumeister household (country-side) and its territory which comprises of Wend's home settlement plus 3 villages in the wilderness. 

 

The Margrave Breithilde family is a Rank 4 Marquis family, that Wend's family "serves" under. Basically when Wend was like 1 years old, the Margrave Breithilde led a joint-expedition with people from Baumeister into the demon forest. It basically got annihilated with few survivors. This puts a strain on the Baumeister Knight household (vassals) and its governing lord Marquis Breithilde (fedual lord) because the then Marquis Breithilde recklessly drove into the demon forest despite the difficulties and losses and got everyone killed because he was trying to get rare ingredients to save his sickly oldest son. So the Marquis Breithilde died in the forest, the Marquis Breithilde's eldest son (heir) died from being sick, and thus we have the second son take over as the current Marquis Breithilde. The current Marquis Breithilde is the lord who arranges for the once in a while merchant caravan to travel through the pain-in-the-ass wyvern mountains to provide trade supplies at a loss due to his obligation towards his retainers (Baumeister countryside knight household) of how is father f*cked up. The forced expedition caused a reduction of the men in the territory which also resulted in less manpower and slowing of the development of the frontier towns. I think 100 men from the Baumeister territory went on the expedition. Only 23 came back alive. (The current Baumeister country-side territory population is like 800 people or so).

 

 

So whats basically happening now with the wedding is that is that Wend's oldest brother & father are being cheap asses because they didn't expect the 5th son to actually marry someone of decent peerage. Elric is basically marrying the sole-child of Rank 7 knight Brandt household and will become the head of that household. They basically sent a letter for the 3rd and 4th brothers who left home with nothing and are commoner castle guards, telling them "Hey pay up the dowry in our stead because we did "so much" for you by giving you a small amount of money to make it out on your own in the capital so you owe us". Initially the money that they get for leaving the house is suppose to be compensation for not being able to succeed the house-hold and clear away any bad air. So the Baumeister-household (countryside) has no right to be asking more from the the 3rd and 4th brothers. In  addition, since the bride is coming from a respectable knight household, the dowry is gonna be beyond the means of what castle grunts can afford but they can't be cheap with the dowry because it makes the groom's family look bad.

 

The Baumeister-household (Country) had the option of borrowing money from their lord Marquis Breithilde, but they were too stubborn and cheap to do so. The Marquis Breithilde has an interest in doing so also because if Baumeister-household can't pay up, it makes him look bad because they are his vassals.

 

So now Wend is gonna pick up the slack since he's baller now and rolling in dough even though 3rd (Paul), 4th (Helmut), and 6th son (Wend) have no obligation to be doing this. 

 

The reason why Brantark (Burkhart in the novels) says Marquis Breithilde will pay him back is because the Marquis is going to assume responsibility for this and treat it as "a forced loan to the Baumeister family" and pay Wend for the dowry. This is so he can turn around and hang this over the Baumeister-household (Country-side) and make them pay for it. The "how dare you almost embarrass me other nobles in the capital". As we all know, gossip travels like wildfire and if there was no dowry, it'd embarass the Elric, groom's family Baumeister-household (Countryside), and their lord, Marquis Breithilde in front of all the other nobles.

 

Later in the WN they explain that part of the family left after a struggle and decided to try and create a frontier city. Unfortunately it wasn't as profitable as expected and they incurred massive debt due to another noble's command. The main family excised them, and they really only have a noble rank purely because they own land. The king later on actually thinks about forcibly giving it to the MC so he can remove their noble status, as well as have the MC use his OP powers to cultivate the land

and

was just introduced in the LN. It's predictable enough, but I didn't expect to see LN spoilers on here.