I daresay it’s not impossible to get a U.K. visit visa when unemployed, if you can demonstrate a strong travel history and sufficient close family ties in your home country to convince the ECO that you will leave at the end of your visit. However, without a job to go back to and with family in the U.K., your profile is pretty high risk from an ECOs point of view, as Henning Makholm’s comment above indicates. There is a great schematic here Schengen visa refused from German embassy which, whilst it references Schengen specifically, shows how the ECOs risk assessment of your application might go. If you do apply, I’d suggest you resist the temptation to ask for a long visit, and have a good, provable, reason for it e.g. grandparents’ 30th wedding anniversary or some such. But overall if I were you I’d wait until I had a job in my home country.