Hey, Shell, I'm sorry you're struggling.
It's a little unsettling trying to take a relatively new medication, and it sounds like effexor is still pretty new to you. Try to think about what you fear from it - the brain problems, or even anything else. Do they seem very likely to you, or is it more that fear of the unknown that just won't stop? Did you have problems with lexapro? If not, try to use that memory to soothe yourself - tell yourself out loud that you've been on meds before, and they didn't hurt your brain, so they won't now.
I'm sorry you're concerned about your family life. That's got to be really draining your energy for fighting the health anxiety. Your babies will be able to grow and learn from you, even if you aren't perfect, even when you do struggle. From you, they'll learn compassion, and patience, and how to understand that sometimes the people in their lives don't feel good, and that's okay.
Some of the physical symptoms you describe - the tingling, the leg cramps, and neck problems - would make me head out to see my chiropractor. Stretching and trying to become more flexible can help with issues around the spine too.
Sorry I don't have any more coherent advice. Just want you to know that I care, and I hear you!