Its definitely possible but wiring stuff into minis is not a very nice job 
have you any idea about the cost and know if anyone can fit them ? only 17 so dont want to be mess my pride and joy up haha
I know that halfords can do installations but some of their work isn't great and to be honest they'd probably be stumped with a classic car rather than a nice easy modern car. I would either look around and try to find an independent car audio specialist near where you live, or if you go DIY, put the research in and make sure you know what your doing; it isn't hard to put a stereo in but it has to be done right. I haven't had a stereo fitted myself but I'd imagine cost wise it would probably be fairly steep; It wouldn't surprise me if you were charged £40 per hour for a couple of hours labour.