Winter is coming where I live and although the roads are plowed and salted where I live to the point where many people still drive around with all-seasons, I would like to prepare for the winter. In the past I used a second set of wheels to put on winter tires but perhaps this was not necessary. This year I would like to try these new generation 'all-weather' tires (something like general altimax 365aw or maybe crossclimate2 althought those are expensive).

The issue is that my back tires are old and need to go but the front tires (ecopia) still have 6/32 on them. I had hit a curb and popped a tire last year so I had to replace the front ones but the rear ones stayed on but are now too worn to keep.

Should I just buy 2 new tires and only replace the 2 worn tires (and swap them to the back of my fwd) car or should I replace all 4? How unsafe/bad would it be for the car to have 2 tires of a different brand, type (all weather vs all season) and age/wear?