i was wondering if i shud get new tires on one of my bikes. its cracked all over the tire, yet it holds air. whats the best thing to do?

the air is holded by the inner tube not the tire itself actually unless you are running tubeless....u should get a new pair just in case...just like car tires...if they start to crack (doesn't mean threads are gone) but you should replace them. But I have cracked tires and I still do stuff on the mountain no problem....its just more traction on new ones

Yeah it seems like you need new tires, however I can't really suggest you a pair since I don't know what kind of riding you do, however I can tell you Kenda's Blue Groove Front and Nevegal Rear are a great place to start, they have sizes from 1.95 to 2.50 and they come with folding/kevlar/wire beads and DTC or Stick-E compounds so there are a lot to choose from.

Dry rot is never a good thing when dealing with rubber. Get a new set, your tubes will thank you.

"I can tell you Kenda's Blue Groove Front and Nevegal Rear are a great place to start"

is that a brand or what?

yes, kenda is a brand, a good one. get new tires if you are starting to get lots of flats

If they are cracked then you should definitely change them. Rubber loses its grip ability over time and cracked rubber is typically a sign that the rubber is too old.