Are you wanting
to change this particular relationship with this couple from a swinging thing to a polyship?
If so, ASK.
And if they are willing, let them know what your wants, needs, and limits are in a polyship. Ask them what their wants, needs, and limits are in a polyship.
Maybe they want to have a serious polyship with you, but be OPEN to swing still on the side. Maybe they will only polyship if all are CLOSED. Are you willing to stop swinging if so? There's a lot of "maybe" to discern and get nailed down.
So if a polyship is what you want with them now, you have to ask them directly if they want that too. You cannot mind reader them, they cannot mind reader you.
Also, if it isn't typical, how do we go about navigating the first quad relationship landmines that could screw up a great thing. Does "date you guys" mean see each other more often and keep the emotions casual, or deepen the emotions as the course of the relationship unfolds?
after behavior. You do not actually control emotion like a faucet. On/off. You do not "keep the emotions casual" or "deepen the emotions." You engage in behavior that then results in these feelings. First behavior ensues some feelings. Now can choose next behavior in response to those feelings. You get to choose -- Keep ON doing the thing or stop doing the thing?
What quad landmines are you worried about?
That I valued them as people more than FWB so I still wanted to spend time together. They were dumbfounded, assured us that was not the case at all, and said they would do their best to do their eat to be more available. So far, not much improvement but there is effort. A bit. I still feel that we are chasing them harder than they are excited about seeing us.
When you asked them for more time/attention -- was that clearly communicated?
"I want more time and attention from you because I would like to develop and grow a polyship with you."
Or could they still think it is at the place of
"I want more time and attention from you because I like to swing with you."
Time doesn't appear from the sky. People MAKE the time to spend in cultivating relationships. Maybe they figure the time they spend on cultivating your swingship is plenty and don't realize you now want to cultivate a polyship.
So... speak up. That's the only way to know for sure -- you ASK them and they respond so you can KNOW. If they are not up for a polyship, they just are not up for it. Accept it. Then choose the new behavior. Keep swinging after knowing this new info, stop swinging with them after knowing this new info, or swing at a less frequency, or something else. YOU choose how to behave.