I think you should work on the night sleep first, because the success happens more quickly than day sleep. It's just more encouraging to start with the easier one first. The nursing is a bit excessive. It sounds like they are wanting to nurse after every nighttime sleep cycle because they don't know any other way to fall back to sleep. This is the reason they protest if you don't nurse. The reason behind sleep training is to teach your children to fall asleep and stay asleep on their own. It's not easy listening to them cry, but every sleep training method has some crying involved.
The ferber method- You can do scheduled checks during the crying-you would check after the first 5 minutes, then 10 minutes, then 15 minutes, etc. You would be there, but you wouldn't pick up or hold the babies, just show them you are there and leave the room until the next check. Some babies respond well, and others get really worked up over it. They are going to expect to be nursed, so it's better if you have someone else (dh) who can go in the room for the checks. You would do this until the first scheduled feeding. This generally takes more nights than "extinction", which is Weissbluth's method of not going in at all until a feeding, but you need to do what you feel most comfortable with.
At their age, the first feeding should occur 6 hours after going to bed, and 4 hours for each additional feeding. The halfhearted nursing tells you that they aren't hungry, and the excessive wakings can lead to chronic overtiredness leading to more nightwakings. It's a vicious cycle.
Even though you may be starting night training, you can still get a nap routine started . Do the same thing before every nap everyday. At this age, the first nap should occur about an hour and a half after first waking in the morning, and each additional nap two hours after that. This is just a guideline, but I know those who have twins like to get them on the same schedule of course. In another month or so, they will probably be able to stretch another 30 minutes for each naptime. Until you start naptraining, you should do whatever you normally do to get them to sleep.
Hope this helps and if you have any other questions, feel free to ask

.