I think your English is fine. This is great that you are helping your friend.
Now the answers to your questions are as follow:
1. Desferal as you are aware is given using the pump overnight. The long term side effects of desferal are well known and this is considered as safe drug. Desferal has been in use for the last 40 years or so. Exjade, on the other hand, is relatively new drug, it came out 4-5 years ago, short term side effects are known but long term side effects are not known. Most of the children on this forum are using exjade, as it is easy to use (dissolve tablet in water or orange juice and simply drink it), I do not believe there are any major issues with exjade so far. I cannot comment if using desferal two times a week is enough, it all depends on the ferritin level of the child. Also, the parent can decide if they want to switch to exjade. The important point is to have low ferritin level in the body and both drugs do the job well. Please talk to the doctor if they want to switch to exjade.
2. It is very common for children to be listless and eat less as the blood transfusion date approaches, It is normal. I do not believe there is much she can do to improve this situation. I would let the child rest and go with the flow.
3.This is a very common dilemma in most societies; it is unfortunate but a reality. My advice is to raise the boy just as you would raise a normal kid. One thing you have to understand and let the mother know that thalassemia may sound terrible, but in modern days, thalassemics are living healthier, successful and normal lives. They are getting married and have children of their own. Do not bother trying to explain a three year old, he would not understand. When the time comes he will understand. Just raise him like a normal kid. Just keep up with the blood transfusion, iron chelation and manage the situation.
Now, I also suggest you keep coming to this forum and ask any question and we will answer.
Please convey to the mother that help is available.