Yes, peat moss and coco coir can be mixed together. They are both great additions to soil and combined would offer lots of benefits. Together they will boost the water-retention capacity of the soil and both improve the drainage and aeration.
Using coco coir with the peat moss will lessen the acidity of the peat moss, which will be beneficial to the plants who would rather a more neutral pH. It is recommended to test the pH of soil to help you get the right level for your plants and it can be done with a simple soil test kit, available from Amazon