I don't understand why you want to "date" (fuck?) both of them if you're only attracted to one of them sexually. Dating a couple is loaded with landmines.
Do you fear since they "do everything together" they'd only date you as a unit also? But wouldn't the one you aren't attracted to sense the disparity of your interest? How would this all play out, in your mind? Do you imagine 3way sex where you only touch the one you lust after? Why not one on one sex?
Before you make any moves, ask yourself why you want to date THEM and not just the one you really want. You could have the one you really want as a gf, and her wife/partner as a metamour/friend. 3way sex is not the only way to go... and might feel hypocritical, if you're just doing one girl to get at the other one...
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 59, living with:
miss pixi, 37