Tire replacement question...

[PeteG]

I currently have my snows on the X5, which i keep on dedicated rims. I went downstairs to peek at my spring/summer/fall wheels in the basement to see how they were wearing (Had an alignment done back when I put the snow wheels on in December).

Here are the tread depths I found:

1) 8/32
2) 7/32
3) 5/32
4) between 4 and 5/32

By the way, the tires are all the same size, Michelin Energy's 255/55/18.

Any suggestions on how I should replace these? I'm thinking of keeping the first two with the most tread and getting 2 new (2 new on same axle). Is that a good idea? Will this throw off the balance in or affect alignment in any way? I'd love suggestions.

Thanks!!!