i think recommended age gap is currently 3 years, friends of ours are going through the process with a bc and this is what they have been told, but i think they see sibs/ half sibs differently, ours only have 27 months between the three of them and we adopted them all separately, squirrel placed in feb 2012, howler in august 2012 and george in nov 2013, so this rule is def not set in stone.
i think 3 years is so that the children are in separate stages and the theory is that they will be less competitive as their needs will be different and the older child is able to rationally understand why a smaller child might need more of a parent's physical attention.there would be less comparison as they would be at separate stages and less interest in each others property. the older child (if adopted) would have had time to become established in their placement, be more secure with their parents and able to be reassured and comforted y them, and for adoptive parents to have a good idea of what their child is like, how they are likely to react to change and how to best help them with this.
practically if there is a three year gap, the older child is likely to be in school/ nursery already, giving parent one to one time with new lo while settling in and giving siblings some time apart as being together all day everyday can be v intense for sibs. older child is likely to have a different bath/ bed schedule giving them special time at the end of the day. older child also might have developed positive relationships with wider family and support network so that they can be helped by other members of the family as new child settles in. also i think they think that parents have passed the honeymoon phase with their littlies and know that they enjoy parenting and are secure in enough in their parenting skills to reliably assess their ability to parent a new child. what they want is a secure match, they fear placing a child with an existing ac and the worse case scenario being things going so wrong that one or both children return to care more traumatised than before... so they want to be v sure that you are realistic about what you are taking on and confident that this is the right move for everyone in your family. also when they are older, teenage time is when a lot of underlying stuff kicks in, so you could be dealing with v big difficulties in your aks at the same time
having said this... we adopted three times in less than two years and it has worked for us, i have three littlies with me all the time and in some ways i think it is easier having them closer in age because:
we can do the same activities/ go to the same places
i see them all as v little children and don't put too much on the older ones expecting them to be responsible for the younger ones
the older ones understand their adoption in a v clear way because it has been modelled for them with george's arrival from foster care
they do everything together and have bonded more quickly as a result, they know their is something v special about their little unit
they amuse each other and play together
they learn from each other, howler's speech is phenomenal for her age because she shares a room with squirrel and they chatter all the time
it was v easy to potty train howler as she had watched it all with squirrel
they are learning to socialise and resolve conflict kindly, and be patient naturally, because they have to be!
their interests are extended as they feed of each others passions and ideas
howler settled into nursery v quick because squirrel was there
i haven't forgotten anything as i have only just finished a particular stage eg weaning etc before doing it again more confidently.
they are likely to process their adoptions ata similar age, you won't have a 15 yr old dragging a 6 year old into things they are not ready for
they are reassuring for each other, i can leave george more easily than the girls with a family member, earlier in placement with the girls because he knows its ok if they are their too
mine are a different ethnic mix from dh and myself so have each other who share each others ethnicity and adoptive status
they have v similar stories as bm was in exactly same place for all of them,
i can have them on the same schedule and get down time for myself to recharge
they eat the same type of food
i tend to do the same momento things for them,eg they all have a memory box and i am doing it at the same time, putting the same type of stuff in , so hopefully it will feel quite equal later on.
the thing i most have to watch in myself and others is the tendancy to compare howler (3) and squirrel (2). squirrel is so confident, pretty much the same size and they are both girls and look like twins, that i have to remind myself and others not to expect howler to be three and to be as excited by each milestone and find it as magical.
hope this helps... i think with siblings it really is case by case. only you know your little one and whether or not you instinctively feel they (and you) are ready
exciting times for you