LOL They may expose their bellies, but I am wise enough NOT to rub them! I am to attached to my fingers. Probably why they expose them, because they know I understand they do not like their bellies rubbed. Their heads yes...
You have some very pretty feral cats. Mine are the same pat their heads but no belly rubs. Looking at Stryker with his belly showing he looks like he has some Bengel in him.
They are lucky to have you to care for them