Dad had 2 stents replaced in rca, now he has dyspnea, could this be due to lcx occlusion which he has as well or to heart trying to adapt to b supply ?

It is more: likely congestive heart failure caused by ischemic cardiomyopathy or medication side effect. He needs to see his cardiologist asap.

Chest pain: Any patient with a recent onset of chest pain/shortness of breath who may be potentially unstable based upon history, appearance, or vital signs, should be transported immediately to an emergency department. Heart attack/restenosis needs to be ruled-out.