stingrays in a 75 gallon?

no rays will fit in a 75 for life, and teacups isnt a type of stingray it is a name wholesalers use for small cheap rays because when they are babies they look like tea cups.... these fish will grow at least 18-24" disk size and that is not including tails.
You will need to upgrade your tank

motoros grow up to 12" in the first year, retic stingrays (very hard to get eating after importation) are slower growers but....