I don't understand how any court, even the Supreme Court, claim it has the right to judge which constitutional ammendmeent is legal, and which not.
By the nature of a constitution and its ammendments, everything contained therein is the basis for the legality of everything else.
The court has the duty to interpret the constitution, and may consider any laws to be legal or not, according the the constitution.
But as far as I am aware, only Parliament (Upper and Lower houses) has the power to ammend the constitution, (In Pakistan, this is with a two-thirds majority in both houses). So when an ammendment is passed, courts have no option but to submit to it, and have no right to hear a petition contesting th eir legality.
If there is something wrong with the constitution, it is the duty of the party in power to legislate, and ammend the constitution, if it has enough backing in Parliament.
That depends on the country and the courts.
The court could rule that the government that passed the rule was illegitimate or find faults with the process in most countries.
In countries with common law the court can interpret things with a lot of freedom. In India the courts ruled that the right to equality meant that the reservations up to 50% was OK, but no further. (The number 50% came from courts interpretation, not from anything in the constitution). In US courts first thought that right to equality and slavery were both OK together. Then they said all men are equal but must be separated (segregation), then courts said segregation is against right to equality. It could also say that the constitution is internally inconsistent and strike out whatever provisions it thought was wrong.