2 apple ids

OK so I have no idea how this happened but at some point I ended up with two Apple IDs. I think my first ID was back when there was still the me.com and I had to keep that email address after that basic service went away because I have so much stuff associated with it and have no idea how to transfer it. So I guess it kept that separate Apple ID. I use a different address however for my main Apple ID. Hadn’t really even thought about it until I tried to use FaceTime. My iPhone primary is my “newer”ID and that’s also associated with my iPad. However FaceTime on my phone is using the old one and FaceTime on my iPad is using the new one. I don’t want to delete my old account because it will take away a lot of emails that are critical and I have no idea how to correct this or if I can