make them all have different ip addresses, assign them all in the routing table as default route with the metric being different, whichever one has the lowest w

make them all have different ip addresses, assign them all in the routing table as default route with the metric being different, whichever one has the lowest would be chosen first, if that one is down, it should choose the next one with the second lowest metric. So, you can set 192.168.2.1 as metric 100, .2 as metric 200, .3 as metri 300