My husband and I are poly. We've been together since HS and we talked about it a lot before deciding to try and meet people. Well, I met this wonderful girl and I have been dating her for a while. My husband likes her as a friend, and she likes him as a friends as well. However, I'd really like our relationship to include all of us, like we're all in a relationship with each other. Do you have any advice or tips on how to bring it up with the both of them without it coming off weird?
You can't 'want' two people into a relationship. It's fine for you to have a best-case scenario, a daydream, a fantasy, a wish - but two people will either have feelings for each other, or they won't. Just because it's ideal for you doesn't mean it can happen, will happen, or is the best for everyone else.
It's fine to bring it up as a hypothetical, saying something like "Hey Jeremeth, you seem to get along well with Clotilda - would you ever be interested in dating her too?" And then again with Clotilda. Bring it up when you two are alone, so no one feels pressured or awkward.
If they don't seem interested, it's best to drop it. Your desires don't really factor in here - they're two individual people who can want what they want. Don't make it sound like a suggestion or a request. It's not their obligation to try and conjure feelings for another person just because that would make you happiest.
Think through why you want this and whether you can meet those needs and desires another way. Recognize and honor the intimacy they already have as friends, and ask yourself what's missing from that that you're wanting. If it's physical intimacy, consider finding someone interested in a threesome. If it's deeper, more investment in the relationship, continue including her, doing things together the three of you - but recognize that you may not be able to get everything you want from this person and this relationship, if it turns out that they're both not interested in this arrangement.