1A. 你在这儿学习, 生活都还可以吧? B. 在这儿的生活(上), 还可以, 可是我觉得学习太难了. Delete 上, 在...上, this structure is kind of formal, which is obviously not suitable here, a casual conversation, right?
在这儿的... is enough to express what you need.
2A. 你觉得这件事情应该怎么解决? B. 在解决这件事情上,我没有意见。
解决这件事情,is not an aspect, an angle of considering things.
So, it can't used with 在...上 (in... aspect)
How to fix it. Easy. We just need to delete 在解决这件事情上. No need to repeat this part since both parties know what you are asking and what you are answering to?
This is just a short conversation, short asking, short answering. Concise is also important in our daily communication unless we're writing a composition for a test trying to meet up the demand for the number of words when we were at low grades of primary school.
Believe me, most of us did these kind of thing, try our best to write a long passage with unnecessary words.
3A. 老张这个人怎么样? B. 在身体上他很好,可是在他的商业上不怎么好.
“在身体上” is too serious, too formal in this case. We can say 他身体很好.
可是在他的商业上不怎么好. ”在 他 的 商业上“, order thing, 可是他在商业上不怎么样。