Would I do it? No. Can you do it? Sure.
I would be doing A-B-C linking strategies and putting each on their different IP's if your plan was to grow them.
However, I prefer putting all of my sites on their own IP when I can. If these are not being grown, are not making money, or are of little value. What you are doing now is fine. I would not put much more effort into them, unless you are realistically trying to scale them up in some way.
