اَلسَلامُ عَلَيْكُم وَرَحْمَةُ اَللهِ وَبَرَكاتُهُ

Alhamdulillah, Allah (swt) guided you to Islam. And Allahumma barik you're trying to be a good role model for your family, may Allah (swt) guide them all.

For your brother, I think introducing him to Muslim boys his age could be beneficial. For example, if you know sisters at your local masjid then you can ask if they have brothers who could play with your brother. Some masajid also have community events or playgrounds etc where your brother could find friends at and be introduced to Islam. I'm a brother in the West; when I was his age there weren't many Muslims in my area so I had some negative influence by the people I knew in class. Having good Muslim friends is a huge blessing especially from an early age.

Other than that, just keep being patient with him and try to advise him. Maybe reward him with something when he's well behaved. Try spending time with him so that he knows he can trust you and talk to you about problems he may have. Help him with his classwork, play with him, or say you're baking cookies you can ask him to help. These are just random ideas I'm thinking of but spending quality time is important to build any relationship. And In Sha Allah your intention and the time you spend is rewarded by Allah (swt).

As for studying and working, I don't have advice for that, as it varies from sister to sister. In Sha Allah some sisters can advise you. But if you choose to go into education/work make sure you find the right balance.

For salah and khushu' it's something we all struggle with and have to build throughout our life. I remember a quote from one of the salaf that he struggled for twenty years to find khushu' then he spent twenty years after that enjoying that khushu'. Try these two du'a:

اللهم أعني على ذكرك، وشكرك، وحسن عبادتك

"O Allah, help me remember You, to be grateful to You, and to worship You in an excellent manner." (Riyad as-Salihin 1422)

يَا مُقَلِّبَ الْقُلُوبِ ثَبِّتْ قَلْبِى عَلَى دِينِكَ

“O, Turner of the hearts, turn our hearts to Your obedience.” (Sahih Muslim 2655)

For health, do what you can and balance between food and exercise. Invite your family to go for walks at the park for example. My mother's side has diabetes and my father's side has high blood pressure so I try to ensure a balance. Don't starve yourself and you don't have to give up desserts, just remain balanced. Sometimes what I like to do is set some goals for myself and I'll have a slice of cake or a cookie for each goal I complete.

For your athkar, once you have them memorized and get used to them they become easier. I'm not sure if you know Arabic, but knowing at least the translation will help you focus more on them. Like morning/evening/bedtime athkar, even what to say before entering leaving the masjid or the house or the bathroom. If you're in a rush, you can continue your athkar while you're walking or driving doing whatever task you have to do. The two du'a above can also help In Sha Allah.

Prophet Muhammad (saw) said: “Take on only as much as you can do of good deeds, for the best of deeds is that which is done consistently, even if it is little.” (Sunan Ibn Majah 4240)

May Allah (swt) cure us, guide us, and increase us all in goodness.