How could I keep my career of my home town

On a family reunion viosa, you usually have unrestricted access to the labour market - thus are formally treated like an EU citizen, which is a HUGE advantage over other foreigners.
Your job chances thus depend on your skills (not least language proficiency), education (are your certs recognised here?), how well you present yourself to a potential employer and, last not least, your luck.
Similarly, you could also further your education here, at university or other schools.

First I would like to say thank you for  your positive and instant response as always you have done for others. I hear a rumour that the competition in finance sector is very tough and I am not sure how much they treat my education and work experience. If there is any one else who had such experience please share with me.

Sorry, I am npot in the finance industry, so cannot help ...

Your profile claims you are a German expat that but everything else you write indicates you are not German. I assume you are Ethiopian and your profile should reflect this.

Maybe there are some niche jobs in finance or banking where English might be used but I find it unlikely lack of basic German is acceptable. And I wonder where you got the information that you don't need to pass the German language test? This is usually required of non-EU partners. The German Immigration site mentions a few exceptions; having children, even if they have German citizenship, is NOT mentioned. But it is recognized that there are hardship cases where one simply hasn't a good possibility to learn German say in a remote place. But then it is required that the language requirement is fulfilled after arriving in Germany.

Thus for both keeping a residency permit and practically any chance at a good job, you will need to learn the language well enough to get by with. And even if legal and work requirements would not make one learn German, not speaking the language leads to isolation and dissatisfaction. One cannot expect to have a happy life in Germany unless they learn at least minimally get along with the language

Although I did not check the wording of the applicable tegulations, I think there might be a difference between language requirements for joining a German spouse and joining German own children.

Actually,  I am learning the language recently  in private institution other than Goethe and I think to take the exam privately. While submitting my document at the embassy the front office staffs told me that I don't need the language proficiency test since I own children. I have got  a good knowledge from this forum German language is  the first step for easing life and I am well prepared for it. I also assume it will takes me a year for intigration. And please consider my question based on this. Thank you once again.