For front wheel drive cars, as you've found out, the fronts wear out but the rears last ages, leading to issues with time-expired rears.
For this reason I always put new tyres on the back, and move the old backs to the front. This is only sensible for 2 to 3 year old tyres, as you certainly don't want dodgy albeit unworn old tyres moved to the front.
As others have said it is quite possible that the leaking is down to corroded or dinged rims rather than the tyres, but if you are lucky it might just be the old valves
I don't mind paying top dollar for premium brand tyres as the extra cost is maybe £200 a set which isn't too bad over 2 or 3 years' motoring. I've been pleased with my "all-season" Michelins, which focus on wet weather grip in our coldish climate and are surprisingly adequate even on snow. Grip when it is slippy is what matters as there is plenty of grip in the dry, even if summer tyres have more. Proper winter tyres are less satisfactory in warmer temperatures, so make less sense in the UK apart from maybe Highland Scots who might get a second set of wheels for their winter