Creating a Unity-Like DrawableObject in OpenGL - c++

Question

So, I am trying to create a class in OpenGL that will make objects very easy to create, delete and orient. The interface would have the standard functions move(), translate(), rotate(), scale(), but also has a few methods related to parenting. I want an object to be able to set a joint to its parent and rotate, scale and transform along with its parents. This would allow me to create essentially a human skeleton from smaller components.
Assuming I have the vertex drawing working (which I do), but I am having a little bit of trouble constructing the MVP for the model here was my thought process. If I just knew how to combine rotation matrices I would be okay.. but I don't think that's possible without quaternions. Anyone know of how to fix or a better way to solve it?
glm::vec3 scaling; //Scale x, y, z
glm::vec3 rotation; //Rotation x, y, z
glm::vec3 position; //Position x, y, z
glm::vec3 offset; //Offset of the connection between the parent and this
Drawable* parent; //Parent connection joint
std::set<Drawable* const> children; //All child connections
inline glm::mat4 getModelMatrixCopy() const
{
glm::mat4 mm(1.0f);
glm::mat4 s(1.0f);
s = glm::scale(s, scaling);
mm = glm::translate(mm, position);
mm = glm::rotate(mm, glm::radians(rotation.x), glm::vec3(1.0, 0.0, 0.0f));
mm = glm::rotate(mm, glm::radians(rotation.y), glm::vec3(0.0, 1.0, 0.0f));
mm = glm::rotate(mm, glm::radians(rotation.z), glm::vec3(0.0, 0.0, 1.0f));
return mm * s;
}
inline void translate(float x, float y, float z)
{
position.x += x;
position.y += y;
position.z += z;
for (auto it = children.begin(); it != children.end(); it++)
{
(*it)->translate(x, y, z);
}
}
inline void move(float x, float y, float z)
{
for (auto it = children.begin(); it != children.end(); it++)
{
auto child = (*it);
float xOffset = (position.x - child->position.x);
float yOffset = (position.y - child->position.y);
float zOffset = (position.z - child->position.z);
child->move(x + xOffset, y + yOffset, z + zOffset);
}
position.x = x;
position.y = y;
position.z = z;
}
inline void rotate(float xDeg, float yDeg, float zDeg)
{
//???? This just seems wrong, need to rotate based on the addition of all previous children
rotation.x += xDeg;
rotation.y += yDeg;
rotation.z += zDeg;
for (auto it = children.begin(); it != children.end(); it++)
{
auto child = (*it);
child->rotate(xDeg, yDeg, zDeg);
}
}
inline void scale(float x, float y, float z)
{
scaling.x *= x;
scaling.y *= y;
scaling.z *= z;
for (auto it = children.begin(); it != children.end(); it++)
{
auto child = (*it);
child->offset.x *= x;
child->offset.y *= y;
child->offset.z *= z;
child->scale(x, y, z);
}
}