Help about 7 segment

just want to know how many multiplexers and what kind are needed to activate 2 7-segment with the common ground at the middle?

thanks

2 x 7-segment displays can be driven directly from a microcontroller. So you need nothing else. The micro will do all the up/down counting, debouncing and remember the count when the circuit is switched off. This is the way to go. See: 2 DIGIT COUNTER, if you care interested.