Reading relationships classical BaZi style is relatively easy once you know the fundamentals of the style.
According to ZPZQ reading for parents, spouses, children from one's chart is somehow accurate but reading for siblings from one's chart is often inaccurate. The closer the relationship, the more accurate the reading can be. Parents, children and spouses are considered close while siblings and ancestors are not.
原文：其由宫分配之者，则年月日时，自上而下，祖父妻子，亦自上而下。以地相配，适得其宜，不易之位也。
Year EB represents ancestors
Month EB represents parents
Day EB represents spouse
Hour EB represents children
It's a principle that does not change
As for matching the Useful God with the relationships, Direct Seal is mother, self comes from Direct Seal, as it engenders Self.
若偏财受我克制，何反为父？
If Indirect Wealth is countered by Self, how can it represent father?
偏财者，母之正夫也，正印为母，则偏财为父矣。
Because Indirect Wealth is mother's true husband (Direct Seal's HS combination), thus it is regarded as father.
正财为妻，受我克制，夫为妻纲，妻则从夫。
Direct Wealth as wife, as it is countered by self, husband is the outline for the wife, wife follows husband.
若官煞则克制乎我，何以反为子女也？
If the authorities counter Self, how can it be regarded as the children?
官煞者，财所生也，财为妻妾，则官煞为子女矣。
The authorities are engendered by Wealth, Wealth represents wife or concubine, that's why.
至于比肩为兄弟，又理之显然者。
As for parallels representing brothers, the logic is apparent.
To know if one has the support from any of the relationship, it is auspicious or inauspicious, it has to be analyzed from looking at what is contained in the chart and match them to the six relationships.
局中作何喜忌，参而配之，可以了然矣。
Then look at the overall structure, match with the Useful God and one can naturally know.
Easy right? Not really,
Well let's take for example, reading for wife. How do we know if one could get a good wife?
When the DM sits on Wealth or Officer, then one gets a good wife, but there are cases when the DM sits on Wealth or Officer but the wife is not beneficial, on the other hand, there are cases when DM sits on Hurting Officer or YangRen but the wife is auspicious, why?
既看妻宫，又看妻星。
此盖月令用神，配成喜忌。
That is because it has to be matched with the YongShen from the Month Command to determine auspiciousness.
如妻宫坐财，吉也，而印格逢之，反为不美。
For example, the wife palace contains Wealth, it is auspicious, but when the structure is Seal, it becomes not auspicious.
妻坐官，吉也，而伤官逢之，岂能顺意？
The wife palace has Officer, is originally auspicious, but when the structure is Hurting Officer, how can (the marriage) be smooth?
妻坐伤官，凶也，而财格逢之，可以生财，煞格逢之，可以制煞，反主妻能内助。
The wife palace sits Hurting Officer, is inauspicious, but when the structure is Wealth, it can engender Wealth, when the structure is Devil, it can restrain Devil, so the wife can support (within the family)
妻坐阳刃，凶也，而或财官煞伤等格，四柱已成格局，而日主无气，全凭日刃帮身，则妻必能相关。
The wife palace sits YangRen, is inauspicious, but if the structures (i.e Wealth, Officer, Devil, HO etc) are already completed but the DM is without Qi, then the DM relies on the YangRen of the Day pillar to assist Self, thus the wife must be really supportive.
Looking at the wife palace, also look at the wife star (Wealth)
妻星者，干头之财也。
Wealth star, is the Wealth from the HS.
妻透而成局，若官格透财、印多逢财、食伤透财为用之类，即坐下无用，亦主内助。
When the Wealth protrudes and complete the structure,
e.g
Direct Officer structure with protruding wealth
Abundant Seal with protruding Wealth,
Outputs with protruding Wealth etc
even when the Day EB is of no use, it also denotes getting internal support (from the wife)
妻透而破格，若印轻财露、食神伤官、透煞逢财之类，即坐下有用，亦防刑克。
When the Wife (Wealth) penetrates and cause the structure to break,
e.g
Seal is light and Wealth is exposed,
Food or Hurting Officer,
Protruding Devil and seeing Wealth,
Even though the spouse palace is useful, one still has to beware of (punishment or countering)
又有妻透成格，或妻宫有用而坐下刑冲，未免得美妻而难偕老。
Also, if the wife protrudes to complete the structure, or if the DM sits on useful palace, but then it is clased or punished, it is difficult for one to get a beautiful wife and it is difficult to grow old together.
又若妻星两透，偏正杂出，何一夫而多妻？
Also if there's more than one Wife star protruding, Direct and Indirect mixed, can it be one husband with many wives?
亦防刑克之道也。
also beware of the Tao of punishment and countering.
To read for offsprings, the concept is the same as reading for wife.
然长生论法，用阳而不用阴。
但看子息，长生沐浴之歌，亦当熟读，
But to read for offspring, one must be familiar with 'the song of ChangSheng MuYu'
Which is:
长生四子中旬半，
ChangSheng is four sons but after the half of the season, only 2 remains,
沐浴一双保吉祥，
Muyu is one pair and it's guaranteed to be propitious.
冠带临官三子位，
Guan Dai and LinGuan, the place of 3 sons,
旺中五子自成行，
Middle of Wang (DiWang), five children is self-obtained
衰中二子病中一，
Within Shuai 2 sons, within Bing there's one
死中至老没儿郞，
Within Si, until one is old there would be no son
除非养取他之子，
unless one nourishes (adopt) the son of others.
入墓之时命夭亡，
Entering tomb, its life is short or it dies.
受气为绝一个子，
Receiving Qi is Jue it has 1 son.
胎中头产养姑娘，
Within Tai, the first born will be a lady (girl)
养中三子只留一，
Within Yang there's 3 sons but only 1 is left.
男子宫中子细详
For men, analyze meticulously the palace of children.
As for the method of analyzing ChangSheng, it uses Yang but does not use Yin.
如甲乙日只用庚金长生，巳酉丑顺数之局，而不用辛金逆数之子申辰。
As an example, for the DM Jia and Yi, look at the ChangSheng of only Geng metal, which is the forward cycle of Si You Chou and not the reversed cycle of Xin metal which is Zi Shen Chen.
虽书有官为女煞为男之说，然终不可以甲用庚男而用阳局，乙用辛男而阴局。
Although there are books that say Officer as daughters and Devil as sons, one cannot read as though Jia uses Geng as sons so it has to use the Yang structure, Yi uses Xin as son so it has to use the Yin structure.
盖木为日主，不问甲乙，总以庚为男辛为女，其理为然，拘于官煞，其能验乎？
That is because when wood is the DM, regardless of Jia or Yi, Geng is regarded as son and Xin as daugther, the logic is natural, do not stick to Officer and Devil, how can it be accurate?
So, when one gets a set of Bazi, to read for the offsprings, first look at the Hour EB
如甲乙生日，其时果系庚金何宫？
If the DM is Jia or Yi, what is in the hour EB? at what palace is the Geng Metal?
或生旺, 或死绝，其多寡已有定数，然后以时干子星配之。
Is it ChangSheng / DiWang? is it Si or Jue, whether there are many or none it is already destined, then look at the Day Stem and analyze the children star.
如财格而时干透食，官格而时干透财之类，皆谓时干有用，即使时逢死绝，亦主子贵，但不甚繁耳。
As an example, if the structure is Wealth and the hour stem protrudes Food, or if the structure is Officer and the hour stem protrudes Wealth, then the hour stem is useful, although it meets Si or Jue, it still denotes noble children but number should be few.
若又逢生旺，则麟儿绕膝，岂可量乎？
If that meets ChangSheng or DiWang, the one will have many great and capable children (described as the sons of Lin (mythical auspicious creature) surrounding one's knee), how can it be measureable?
若时干不好，子透破局，即逢生旺，难为子息。
If the Day stem is not good, son protrudes to break the structure, even though one meets ChangSheng or DiWang, it will be difficult for the children.
若又死绝，无所望矣。
If it meets Si or Jue, then one is hopeless.
I think ZPZQ has explained well on this subject.
