不想这日三月十五,葫芦庙中炸供,那些和尚不加小心,致使油锅火逸,便烧着窗 纸. 此方人家多用竹篱木壁者,大抵也因劫数,于是接二连三,牵五挂四,将一条街烧 得如火焰山一般. 彼时虽有军民来救,那火已成了势,如何救得下?直烧了一夜,方渐 渐的熄去,也不知烧了几家.

My try:
Unexpectedly at the day of March, the 15th, in the monastery 葫芦 there was food frying for scarifying to the gods. Those monks were not careful enough to prevent the fryer from bursting into flames, then the window curtains caught fire. In this place everybody extensively used bamboo fences and the wooden walls for building houses, probably it was predetermined fate. As a result step by step the street turned burning like a sort of “Mountain of Flames”. Although firemen came for rescue, at that time the fire already had become powerful, how could it be stopped? It had already been burning a whole night, when it was slowly extinguished and it was unclear how many homes were burned down.

Breakdown:
不想这日三月十五
(不想) unexpectedly at the day of March the fifteenth

葫芦庙中炸供,
in the monastery 葫芦(炸供) there was food frying for scarifying to the gods

那些和尚不加小心,
those monks (不加小心) were not careful enough

致使油锅火逸
to prevent the fryer from bursting into flames

便烧着窗 纸   
then the (窗 纸, lit. „Window paper“) window curtains caught fire
 
此方人家多用竹篱木壁者
In this place everybody (多用) extensively used (竹篱) bamboo fences and the wooden walls (木壁者) [for building houses]

大抵也因劫数
(大抵) probably (劫数) it was predetermined fate

于是接二连三, 牵五挂四
As a result (接二连三) one after another, 牵五挂四 (one after another) -> step by step

将一条街烧 得如火焰山一般
the street turned burning like a (一般) sort of (火焰山) Mountain of Flames (also insurmountable obstacle)

彼时虽有军民来救,
(彼时) That time although (军民) firemen [lit: soldiers and civilians] came for rescue

那火已成了势,
That fire already had become (势) powerful

如何救得下?
How to save (=stop the fire)?

直烧了一夜
[Already] Burning a whole night

方渐 渐的熄去
(方) Just/then it was slowly extinguished

也不知烧了几家.
And it (不知) was unclear how many homes were burned down

他岳丈名唤封肃,本贯大如州人氏,虽是务农,家中都还殷实.今见女婿这等狼狈 而来, 心中便有些不乐.幸而士隐还有折变田地的银子未曾用完,拿出来托他随分就 价薄置些须房地,为后日衣食之计.那封肃便半哄半赚,些须与他些薄田朽屋.

I have some trouble with three parts in this section that I marked red in the breakdown.

My try:
His father in law was called 封肃, a native from a place called大如州. Although being in the agriculture business, the family nevertheless was well-off. Now that he saw the son in law hat come in such a difficult situation, he therefore felt very unhappy. Fortunately the money 士隐 got from selling off his land had not yet been used up. He took it and entrusted it to him to get a share which was - under consideration of the market price - a rather small field and house. Preparing for the living later that 封肃 therefore was half cheating, half making money. He gave him a little meager field and a rotten house.

Breakdown:
他岳丈名唤封肃,
His father in law was called 封肃

本贯大如州人氏
That (贯) native place 大如州 [was his] (人氏) place of origin -> He was a native from a place of 大如州

虽是务农,
Although (务农) being in the agriculture business

家中都还殷实.
the family nevertheless was (殷实) well-off

今见女婿这等狼狈 而来,
Now that he saw the son in law hat come in such a (狼狈) difficult situation

心中便有些不乐.
He therefore felt (有些 - “a bit”, I guess this is understatement) very unhappy (in his heart)

幸而士隐还有折变田地的银子未曾用完,
Fortunately the money 士隐 got from selling off his land (未曾) was not yet used up.

拿出来托他随分就 价薄置房地,
He took it (托他) and entrusted it to him (随分) to get a share (就价, “by the price”) – [which was] under consideration of the market price - (薄置) a meager field and house

为后日衣食之计
Preparing for the living later

那封肃便半哄半赚,
That 封肃 therefore was half cheating, half making money

些须与他些薄田朽屋
(与他) Gave him (些须) a little (薄田) meager field and a (朽屋) rotten house