Hi :)
I have 2 older daughters, who are now 27 and 17, and when it comes to contact with their biological parents, they have polar opposite viewpoints and have done the complete opposite to each other(they both however are in contact with siblings)
My personal feeling, is that our role as parents is to support our children with whatever they decide to do, as far as they want us to. If they would like to seek out contact, we support them with that, but if they aren't interested in contact, then we also have to support that. Our own private feelings about what's best can't really come into it, and sometimes that's hard - I know that I wish my 17 year old wasn't meeting up with her mother, but it's certainly not my place to say that to her.
In your situation - no, I don't think you should suggest to your children that the get into contact with their biological parents. Making contact if they haven't had any previously is a really big step to take, and it's something they should only do if they are absolutely sure they want to do that, and are as mature and mentally prepared for it as far as possible. Contact can bring up a huge range of feelings, and sometimes it doesn't go well. It's not something that should be suggested to them. It might seem like a good idea to you, but every adoptee thinks differently about it, and to your daughters, well, they might not want contact at all right now, and it might seem like a bad idea to them.
If you tell them you think it would be good to do something that they aren't comfortable with, then there's a chance you'll create a bit of a gulf between you, meaning they aren't so likely to talk to you about how they really feel, because they will think "well, mum doesn't understand how I feel about this, she thinks the opposite to me, so I won't bring it up with her"
I do think that we should let our children know that we will support them in their decisions. I have told my children that I am behind them and will be there for them whatever they choose to do.
So if you bring up the subject of contact, I would only bring it up as "I want you to know that I support you 100% in whatever you decide to do. I would be completely comfortable and fine with it if you decided to seek out your birth family, and would help you as much as you wanted. Likewise, if you decide not to seek out any contact ever, I also completely support you"