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If I read things correctly, you are:
According to this article (at least my understanding of it) an ECO will not cancel a existing Tier 4 Student visa that you have already used to enter the UK.
You may however be refused entry under paragraph 320, 321 if you try and use your Tier 4 Visa to enter and the IO determines that your change of circumstance invalidates your visa, however this should not happen obviously, as you will be entering as a visitor on a general visit visa.
I am confused as to what you mean by 'proving family ties', in the visit visa application, it does ask you to list the details of your Mother and Father, however there is no requirement to prove this in your application, unless specifically asked to.
What I think you mean is, how are you going to show that family is one of the reasons you will leave the UK at the end of your visit. You cannot prove this, as you already said, because your family lives in Uganda and you do not. Don't worry, this is not something that severely affects your application. If you can prove beyond reasonable doubt via other means (economic ties as you said, for example, like a job in the UAE), then that should not be an issue.
Please correct me if I have misunderstood anything in your question.