All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the reason for breaking the fast is due to diabetes, then you are only required to make up the days you broke the fast whenever you are able to do so. Allaah says (what means): {…but if any of you is ill or on a journey, the same number (should be made up) from other days…}[Quran 2:184]. It is not permissible for you to feed poor people instead of fasting as this is only allowed if the disease is chronic. If a trustworthy doctor decides that you are absolutely unable to fast because of diabetes for being a chronic disease from which you are not expected to be cured, then you can feed a poor person for every day you break the fast. If after that, you recover from this disease, you will not be obliged to make up the days you did not fast, because you are already acquitted by feeding a poor person.
However, if you broke the fast because of pregnancy or breastfeeding just out of fear for your child, then you have to make up the days you broke the fast in addition to expiating for each day by feeding a poor person. Nonetheless, if you are absolutely unable to fast, then you have to feed a poor person instead of fasting.
As regards whether you should feed a poor person instead of fasting and expiate for that as well by feeding another poor person, or that just one feeding is enough, then we did not come across any statement of the scholars is this regard. However, in order to be on the safe side, it is better to feed a poor person for every day you broke the fast and expiate for it as well.
In case you broke the fast because you feared about your health because of pregnancy or because of breastfeeding, or because you feared about your health and your child's health, then you are only required to make up the days you broke the fast, and if you are unable to fast, you should feed a poor person.
With regard to your brother in-law residing with a marriageable woman without marriage, then this is something forbidden. If sexual intercourse took place between them, this is pure fornication and the child should not be traced back to him but to his mother whether this woman is among the women whom we are allowed to marry (from people of the book), or a woman that we are not allowed to marry (like idolaters).
Your brother in-law should stay away from this woman because what he is doing is forbidden and this is well-established in Islam by absolute evidence and no one can deny it. It is not permissible for a Muslim man to marry a non-Muslim woman unless she is a chaste Christian or a chaste Jew.
So your brother and any Muslim who knows about your brother in-law, should advise him and prohibit him according to his ability from this disgraceful conduct.
As regards what you have mentioned about your husband's relatives asking you to supplicate to Allaah to bless you with a boy and not with a girl because a boy is the crown of the head and a girl is the burden of the head, then this is wrong and it is something of the pre-Islamic era of ignorance. However, if they only want you to ask Allaah to bless you with a boy then there is no harm in this and there is no harm on you in doing so, but if Allaah blesses you with a girl then you should not draw on yourself the Wrath of Allaah as whatever Allaah decrees, there is good in it.
Allaah Knows best.