If it is indicated in your Home Study that you desire to adopt siblings of 5-10 years and if you decide to adopt siblings, for instance, of 5 and 3 years old during your appointment at the SDA, the Department won't allow you to adopt them because there is a limitation in your Home Study 5-10 years old. So it is better to indicate the age 0-10 years old in the Home Study.
If your Home Study is already completed, please get an update from your Social worker and agency where they will state you are approved to adopt children of the age 0-10 (unless there is no age limitation in your I-171 H form).
Also I would recommend you to indicate that you may adopt up to 3 children, even if you won't adopt 3, sometimes it is possible to receive a separation form in the region.
Here are general recommendations for the Home Study
If you want to adopt one child, please, indicate in the HS that you want to adopt one child but may consider two siblings in case there are no child available meeting your requirements. If you want to adopt 2 siblings, pls specify that you are open to adopt up to 3 children, but may consider 4 siblings in case there are no child available meeting your requirements like 2 or 3 children.
Please note that it is not allowed to separate siblings under our laws. But this is still possible in some regions and in the best interest of the child. For instance two siblings live in one orphanage together and their third brother or sister is an older child and lives in different orphanage. So in the best interest of the younger ones separation may be allowed.
Also there are more chances to adopt two siblings than one child, and even more to adopt 3 siblings and the youngest children of this sibling group may be 1-5 years old.