Hey Peter,
I didn't quite get your first question, so you'll have to rephrase it, in english if you want. Regarding the Personal Infinitive and the Future Subjunctive, it's not surprising that you have issues with them, since there are few languages with those tenses. However, there are analogous constructions in english so I'll explain using those. I'll start with the simplest one, the Personal Infinitive. First of all, remember that for regular verbs, both tenses are constructed the same way, but it's still important to know the differences
The personal infinitive is functionally equivalent to the form "For + subject + to + verb " in English, same with "In order to", etc and it's most commonly used with the particle "Para". For example,
"In order for them to sleep, their mother has to sing them a lullaby."
Translates to
"Para eles dormirem, a sua mãe tem de lhes cantar uma canção de embalar",
Where "dormirem" is in the personal infinitive, third person plural.
On the other hand, the use of Future Subjunctive is equivalent to the type I If-clause in English and is used to express the consequence of actions which haven't happened yet. I'll give another example. The sentence
"If he goes home, he's going to sleep"
translates to
"Se ele for para casa, vai dormir."
Where "for" is the future subjunctive form of the verb "ir", third person singular.
I hope you understood their use with these examples. It's hard to be more thorough in my explanation using a tablet! If you have further questions, drop me a message.