In this case, you should ask your friends to accommodate you. If the husband is driving, your husband could ask to sit in the front to have more legroom. Or he could say that he is feeling a little nauseous and would appreciate an opportunity to sit up front.
If the baby is not present for the ride, you could also ask them to remove the seat for your comfort. (Promising to help them reinstall it on arrival might help convince them.)
If it turns out that the back seat is spacious enough for the two of you to sit next to each other without necessarily touching, then you can sit together if there is no better option, as long as you place a substantial item such as a purse between you.
If there is no alternative (or alternative ride), you could subtly explain to your friend and let her do the maneuvering for you. If none of these suggestions can be worked out, it is better not to accept the ride.
If there are extenuating circumstances and none of these sugestions seems workable, please get back in touch with us, or your local Rabbi or Yoetzet Halacha, to discuss further ideas for troubleshooting.
Behatzlacha!