All three of these cactus are the same, the first two were babies from the last one in clay pot, Anyone know what they are??? Thanks for your help! Here is a different one which I have no idea what is also:
The second looks like a Euphorbia as well (of a different species, though). To check, see if it exudes milky white latex when pricked (caution: Euphorbia latex is poisonous and can cause skin burns, don't get it on your skin!). Opuntia have clear sap.