Teach your boy children to put the toilet seat down when they are finished. Remind them and guide them, stress to them the importance of this small gesture. Because it is polite and generally expected, and because you (as the lone female in a household of So Much Penis) still deserve to consistently encounter a properly configured seat during your own visits to the bathroom. And because the habit will carry over and ensure that they will not be viewed as disgusting savages in the homes of neighbors, friends, visiting dignitaries, etc. And lastly, you as their mother will be free to take credit for working so tirelessly to raise three such nice, well-mannered young gentlemen.
Do absolutely none of that, and enjoy up to 20 extra minutes of uninterrupted sleep every morning, as you will be spared the CRAZY LOUD RACKET of a desperate, half-awake boy child rushing into the hallway bathroom and violently flinging up the seat with a RIDICULOUS CLANGING BANG that wakes you up EVERY GODDAMN TIME and thus signals that yep, the kids are up, the toilet seat just woke the baby too so you might as well get out of bed, WTF.