Although I am not expert and related to engineering sector but after reading your emails, I suggest that

Leaving Banking sector at this stage is premature decision, although you are selected for BS-17, but this is not permanent job, and no-one can predict for CSS/PMS or even for this BS-17 job,

You have also mentioned about married life and financial constraints so its unwise to leave Banking job, you can switch in the same sector by getting some good opportunity

Political crises and if new government forms, there is uncertainity about BS-17job

So go for Banking sector, and try to switch job to any financial or multinational company HR job

Much more previliges and facilities in this sector not imagined in CSS or PMS jobs

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Thanks and Regards
M.Zaman
Operations Engineer