Legal Guardian In Case Of Death

I may be overthinking this. Please let me know. My husband and I are planning to set up a will. We were going to name his sister and her husband as legal guardians for our kids in case of both of us dying. My husband just talked to his sister about it today, and she agreed. The problem is, she informed my husband that they are already named legal guardians in case of death for another family with 4 kids. My husband and I don’t have any other options to choose from. We have no other family or friends who could take in our kids. Is it legal for his sister and brother in law to agree to be the legal guardians for two different sets of kids? I realize the chance of them actually taking on guardianship of both families is extremely low, but this situation makes me uncomfortable nonetheless. Would a judge even allow them to take custody of 2 sets of kids? I feel like his sister should prioritize our kids because they are blood relatives. The other family has other relatives they could have named.