While theoretically possible, it's also risky. As far as pens go, it'd be easy enough to build a large pen with lots of land area and a large water area that is easy to walk in and out of (for the easterns), and make the water area deep and large enough for the Malayans... so the physical needs of both species could be satisfied.
It's just a matter of wether or not you want to take on the risk of killing of some or all of your animals in order to mix them. If you choose to risk it, visits to the vet would be a good way to lessen the risk. General de-parasiting and clean bills of health from the vet would be a good start.