Is it permissible to offer mandatory prayer while sitting?

All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions.                                                                                                                                                                                                                            Standing up is a pillar in the mandatory prayer and the prayer is not valid without it unless one cannot do it. As for Nafila (supererogatory prayer), one can perform it in the state of sitting even if he/she can stand, but his/her reward is half the reward of the person who prays while standing if he/sh has no legal excuse for such an act. And Allah Knows Best.

Is my son who was breastfed one filling time by my aunt considered a brother to her children?

The baby who was suckled five sporadic times by a woman is considered a son/daughter of hers.

Is a menstruating woman obliged to pray during menses, and should she make up missed prayers?

All perfect praise be to Allah, The Lord of The Worlds                                                                                                                                                                        A menstruating woman is prohibited from prayer during her menses, and she isn`t obliged to make up missed prayers. And Allah Knows Best.

I became ill while fasting and had to take an intramuscular injection twice on two consecutive days during Ramadan. I continued my fast as usual, as I was told that intramuscular injections do not break the fast. Please advise me so that I can know the correct ruling.