Wow that is a very small cage , when you consider what birds you have. This size of a cage is barely suitable for just one cockatiel and too small for one IRN, I have not tried to work out the proper size of cage for a lovebird, but the cage that I have for my parrotlet is pretty close to that same size, but I would not try to keep two of them in it without plenty of out of cage time. Birds are a lot like people in many respects and this is one of those areas. When they are overcrowded then they are always more fearful and aggressive just the same as people that live in ghetto and slum environments are. You should give this some heavy consideration as there is room for a lot of improvement in this area. You can get by with smaller cages provided that the birds using that cage get enough time out of their cages by which I mean that they mainly just use it for sleeping in.
The diet that you are currently feeding your birds is sort of like the one that was being fed to parrots a little over 20 to 25 years ago and the birds that were fed this type of diet did not live even close to their normal lifespan. They kept dying from liver failure, heart attacks, kidney failure and believe it or not diabetes and pancreatic failure. This was the diet that led to the development of pellet which at first was not much of an improvement.
Since that time there has been a lot of progress in this area. The actual starting point for understanding what and how to feed each of the species of parrots that you have is to do some research to learn what it is that they actually eat in the wild. From this information you can begin to see what types of food that you need to give them as well as when to feed them what foods. Parrots need to be given breakfast, with a little bit of food available to them all day long and then they need to have a good dinner in the evening.
I think that the best thing that I can do to begin to help you to improve the diet of your birds is to give you a link to a list of foods that are good and bad for them. This list also has listing for plants and trees and woods that are both safe or toxic to them as well as a list of some household items that are dangerous for them. The actual lists start on the second page of this link, it would be a great thing to make a copy of as even after 5 year with my birds I still refer to it on a regular basis. Here is the link
viewtopic.php?f=8&t=12521 I want you to understand that we have all made a lot of mistakes in our time with our birds and there is no intent to make any judgements. I think that I need you to understand this right from the start as it is normal for me to try and help you and your birds to improve the areas that need it before moving on to things like hand taming or training. I find that it normally works out best this way as it is very difficult to try to interact with a parrot that does not trust you and when they are not given the right care of their basic needs they will usually not trust you, so that is why I work on improving their life conditions first. If you start making the improvements you will begin to see at the very least small improvements in their attitudes and behaviors, and these will pave the way for earning their trust.