Slow down and back up.
Question 1: What is your actual goal?
Question 2: What degree do you want and what do you want to do with it?
Re: residency: there are 2 kinds of “residency”. Both vary a lot by state, and you can find the rules online. The first kind is residency to qualify as a resident and the second is residency to qualify for in-state tuition discounts. The first only requires that you move there, and do things such as register to vote, get a state ID, pay taxes, etc. The second typically requires that you have been a tax paying resident for at least a year BEFORE you start getting the discount, and some states say that if you have moved there for educational purposes you can never get the discount. This is to stop people from moving to states with generous (taxpayer supported) tuitions discounts (in other words, freeloading).
To answer your specific questions:
Am I considered a resident if I lived in that state for only five years 15 years ago or not?
NO.
If so can I ask someone who still lives in that state to help me get it?
You don’t need permission to move to anyplace in the US. If you mean can you use the mailing address of a friend or relative in order to get the instate discount for tuition, NO, because that is ILLEGAL and FRAUD.
Are there scholarships for Americans living abroad?
Specifically for them? No. Are Americans abroad eligible for scholarships? some.
In the country that am living most of the tests that you need to pass if you want to study in the usa and this is for international students they need to pass TOEFL or GRE do I need to pass them both plus SAT and ACT too?
SAT and ACT are for students applying to undergraduate programs.
TOEFL and GRE depend on the specific program(s) you apply to.
If I want scholarship and financial aid I need to have good score of all the four tests?
As above, not the SAT & ACT, as you are already in university. For TOEFL & GRE, it depends on the specific programs
What about taxes what do I need to know about them? And what if my parents didn’t pay them for years i cant have financial student aid ?
*All US citizens, including you, once you are 18 (younger if you have taxable income) and your parent! - have to file US taxes every year, whether you owe any money or not. And the IRS takes that VERY seriously. But, those taxes don’t help for university unless you are also paying state taxes.
If you apply for financial aid you will have to provide financial documents- ie, tax returns.*
one of my parents is a us citizen the other isn’t does it effect me?
No.