Can we use 2 Time Capsule at the same Time ?

Yes.. you can connect one to the other.. but what do you want to do with them.

A TC cannot backup itself to another TC.. you can manually backup but that is next to useless. It has to be a full backup.. so you cannot use rsync type incremental auto backup.

TM cannot backup network drives.. so you cannot use that for backup of one to the other.

In Mountain Lion you can have multiple targets for TM backup.. so it can use one TC then the other.. this is of course sequential not simultaneous.