Wa ‘Alaikum Salaam sister,
Even though you seem to present this as two separate issues – trying to pray more and refraining from sins as well as feeling depressed that your family doesn’t care for you as much as they do for your siblings -, these issues actually seem to be very much related to each other and could potentially be the cause for a cycle of negativity.
Your feelings of sadness about your family situation will naturally cause you to neglect your Islamic obligations which, in turn, only makes you feel even more sad because you know you should be praying 5 times a day. This then puts you in a negative mood which will make you interpret your home situation in a negative way and so the cycle continues.
Overall, this seems to make you feel negative towards yourself; that not only are you failing in front of Allah (swt), but are less favorable to your family, too. Based on this, it would seem that the solution for you to feel happier at home and more confident in your deen (and, therefore, confident that Allah will forgive you because He can, and He likes to forgive, if only people ask) is to boost your self-esteem and self-confidence, to feel good about yourself.
If you feel better about yourself, you will be less likely to interpret your families’ actions as being more favorable towards your siblings. This boost in self-esteem and happiness will make you more positive and motivated towards your prayers, too.
In regards to your parents’ attitudes towards your siblings, ask yourself what evidence you have to suggest that they do favor them over you. Also, take a step back and see the moments when they do treat you just the same as them. Sometimes, when you get stuck in the feeling that they are favoring others, this is all you will see and you might even be over exaggerating their heightened love towards them over you. If you take a step back and look at things more rationally, you will likely find that this is not the case at all and is just due to distorted judgements on your part because you feel bad about yourself, partly because you are not fulfilling your Islamic obligations amongst other reasons. Think about if they truly are favoring your sibling over you. What evidence do you have? And if they are, is there a reason? Why might they be showing them more love right now? Are they facing a tough time? (For example, in your brother’s case.)
Something else you can do is to do something that makes you feel good about yourself. Set goals and achieve them. See if there is something you are particularly good at. It might be that you do some volunteer work for charity, for example. This will make you feel good about yourself that you are helping people whilst keeping you busy in meaningful activity. This is a meaningful activity that Allah (swt) will certainly look favorably on. Furthermore, doing charity work for the sake of Allah (swt) will help you to keep Allah (swt) in mind more often which will assist you in making sure to pray all your prayers on time as you are thinking of Him more often.
May Allah (swt) forgive you and guide you on the straight path. May He (swt) bring you happiness and ease in your family affairs.
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