The father's rights will likely trump your guardianship petition, unless you can show that he and his sister are pretty bad people. Best answer is probably to offer to take him for extended periods of time, and see if you can get more access by developing a good relationship with your sister-in-law and brother-in-law. If this is not a viable option, the only way you can win in the guardianship battle is to prove them "unfit" which could get expensive and time consuming. These are very tough situations. Good luck.
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