Hmm can't really help, but will be watching with interest.
We haven't started the process yet (our birth child is a little younger than yours) but I had a few initial chats with LAs (we're at the stage where we're looking around to choose which LA/VA we would eventually go with). In one such chat I mentioned that we might consider siblings. The SW immediately (and quite patronisingly IMO) declared that that would never be an option because the two AC would have a trauma bond and would never form a healthy bond with BC.
Just to say I totally understand that this might be a problem, the patronising part of it is simply that the way she said it indicated that she could not imagine that I might have thought about this myself...
Also I am sometimes a bit saddened that some professionals in this area treat cases as numbers rather than considering individual cases and circumstances and the real children involved.
Anyway if you think that you might consider eventually having more than two children, I'd tell them you'd consider it. If you're sure you only ever want two, then tell them no. If you'd like three (or more) kids in total, eventually, then it would be a bit silly to categorically reject siblings at this point.
However if you do 'consider' it, then consider it very carefully. For some siblings it would indeed be best to be placed together, others would benefit from being split. Some siblings' needs might be compatible with having an older sibling in their adoptive family, others might not. But also of course carefully consider what you would effectively be able to deal with. IMO these should be things your SW should help you think through rather than just asking you to decide upfront.
So, in my totally non-experienced view I'd say 'yes we would consider it' (if you think there is any chance at all), so that they help you explore it as an option and you can eventually make a stronger decision for or against.