As a general rule, guardianships are not granted unless:
There are some circumstances where you can get a guardianship over the parents' objections, but you'd usually have to prove that the parents were unfit. You would need a lawyer's help for this.
Other family members -- siblings, grandparents, aunts, and uncles of the child -- are also entitled to know that you are pursuing a guardianship, and have a right to object. You should probably consult a lawyer if anyone in the child's family tells the court that they object to you becoming the guardian.