First, it is not permissible for anyone to ask you to take a loan involving ribā in order to pay for your sister’s education. Ribā is clearly and categorically prohibited in Islam. Allah says: “Allah has permitted trade and forbidden ribā.” (2:275) and He says: “O you who believe, fear Allah and give up what remains of ribā, if you are believers.” (2:278). The Prophet ﷺ cursed the one who consumes ribā, the one who pays it, the one who records it, and the two who witness it, and he said: “They are all the same.” (Muslim). Entering into an interest-based loan is not permitted except in situations of extreme necessity involving life-threatening hardship. Paying for college tuition, while important, does not reach the level of necessity that permits ribā. Therefore, you are correct in refusing to take an interest-based loan, and you are not sinful for doing so.

Second, supporting siblings financially after the death of a father is a noble act, but it is not obligatory upon a brother if he does not have the financial ability. The obligation of financial maintenance (nafaqah) in Islamic law is based on ability. Allah says: “Let a man of wealth spend from his wealth, and he whose provision is restricted, let him spend from what Allah has given him.” (65:7). You are not required to burden yourself beyond your capacity. If contributing would cause you hardship, delay your marriage unreasonably, or place you into debt, then you are not obligated to do so. You may help within your means, but you are not required to equal your brother’s financial level. Fairness in Islam is based on capacity, not comparison. If your brother earns more and has greater savings, then naturally he is more able to contribute. That is not injustice; it is proportionate responsibility.

Third, regarding purchasing a home through ribā-based financing when renting is a viable alternative, the majority of contemporary scholars hold that conventional interest-based mortgages are impermissible because they involve clear ribā. The argument of “need” does not apply when housing can be secured through renting. Therefore, buying a house through ribā is not permissible unless a person reaches a level of necessity that leaves no alternative, which is rare in normal circumstances. The fact that something is common does not make it permissible. Ribā remains one of the gravest major sins.

Fourth, working in a gas station where alcohol is sold requires distinction. If a person directly sells alcohol, stocks it, or handles its transactions knowingly, then this falls under assisting in sin, which Allah prohibits: “And do not assist one another in sin and transgression.” (5:2). The Prophet ﷺ cursed ten categories of people involved with alcohol, including the one who sells it and the one who carries it (Tirmidhi). If your brother is directly involved in purchasing, stocking, or selling alcohol as part of his management duties, then this is not permissible. If his role is genuinely unrelated and he does not participate in alcohol transactions, then the ruling may differ. But direct involvement in selling alcohol is not allowed.

Islam does not require you to destroy your stability to fulfill expectations beyond your means. Help your family with wisdom and kindness, but do not enter into ribā, and do not allow emotional pressure to push you into what Allah has clearly prohibited.