Nancy,
If you back bulbs are soft and brown then they should be removed as they could possibly have a bacterial rot which can spread. It sounds like the plant may have been very stressed before you got it. While Cattleyas normally do not loose their leaves, they may in cases of extreme stress. So...
1) go ahead and remove the back bulbs that are brown and mushy
2) go ahead and repot
3) get a Cattleya care culture sheet either from this forum or from
American Orchid Society so you can give your plant the culture it likes.
With this and a pit of patience, hopefully your plant will be fine.