If it is sure, it is a fact, then there is no need in Spanish to use subjunctive. Ex: Mi hermano llegará -future tense- a las 5. " But in a sentece which expresses a more uncertain situation such as:" No creo que mi hermano llegue a las 5", the use of presente de subjuntivo will be necessary

Lo mejor es utilizar el futuro presente. Pero si dices (he might arrive... puede ser si o no), podrias utilizar el subjuntivo futuro.

"My brother will arrive at 5" Se dice: Mi hermano llegará a las 5. In this case, this is just Future Simple. Actually, we do not use Future Subjuntive frequently. Example: "Sea lo que fuere" - Future Subjuntive We rather say "sea lo que sea". If you want I can give you some resources and help you out with your Spanish.

You'd say "mi hermano llegará a las cinco". There is no need to use the subjunctive here.