A.L.
I have two adopted siblings and I love them both. However, I am the only biological child and I really wish I had biological siblings. My sister was a troubled child and caused a lot of stress and trouble for my parents and my brother and I growing up. I realize this could have happened with a biological sibling, but I really wish I had biological siblings. I grew up in the early 70's and we were the only family I knew that had a mix of adopted and biological children. That was sometimes hard for me as I felt very different, which is hard for young kids. Adoption is definitely talked about more now, so I don't think you would run into that problem.
I can't say if I would love them any differently or more if they were biological siblings b/c I don't have any biological siblings.
I would also say you should really decide how this would impact you, your husband and your kids and decide if this is the right thing to do. Do you want more kids, or are you just doing this so your kids have more siblings? They really are two different issues. Talk to people about the issues you have to deal with when adopting older children, and decide if you can handle that and if it is the right thing for your family.
I'm not saying that it isn't the right thing, just make sure. There are lots of older kids that need homes and it is a wonderful to provide one for them, just make sure it is the right thing for you, your kids and any kids you would adopt.