My parents are Catholic and I'm Southern Baptist. When I visit them I do not take communion because (1)I don't believe it's the actual body of Christ and (2)I don't consider myself part of the Catholic community, even though I was baptized as a baby. My mother isn't happy about it, but accepts my decission. When they visit us, they are told that all baptized believers are invited "to put their feet under the Lord's table" and they take communion, knowing very well that at that time it is just a symbol, a reminder of what Jesus did. We try to respect each others beliefs, but I think it's funny how they are more welcome in our Protestant church than I am at their Catholic one!
I'm pretty sure they are not suppose to take communion at your church.
Your parents as Catholics probably should not receive Communion in a Protestant Church.