Siblings vs health and attachment

Hi all! I'm new here. Hubby and I are looking to adopt two siblings, possibly from Poland, and are wondering if siblings in general are healthier and have less risk of major attachment problems. We have two bio kids, so we are hoping that will help with the family bonding/attachment. We are just beginning the process, so I'm terrified of FASD or RAD. Does anyone have experience with adopting two siblings? I'd like to hear the good and bad. We'd like for both of them to be 5 or younger...is that Possible in Poland? Thanks!