Yes it is. If を is used, I would understand it is an ornate way to say appreciate (understand something and sympathize or value) something.Correct usage is が.
I'm sorry, but this doesn't work like that in Spanish. Entenderse means mainly people getting along: Mi padre y yo ya no nos entendemos. - My father and I don't get along anymore; literally: My father and I don't understand each other anymore.In (3), わかる means 理解する. This feels the same as the Spanish "se VERB" form, like "entenderse". In English, you can't say "I understood myself about the grammar.", but it feels the same.