Hey got more aggre guy questions with you hehehe :D

How would you know if any of them had a crush on you?

Hehe... a classic cute question.

Sans: The absolute most difficult to tell. He just acts like a close pal. Honestly, if you're not Papyrus, it's near impossible to know how Sans is genuinely feeling. This guy is a master at disguise. The signs are ridiculously covert- how many words he uses in his texts, which eye he most frequently winks at you with, the kinds of jokes he uses, which side of you he sits on. He gets slightly jealous of people you like, and expresses that with veeeery subtle coldness toward them. To Papyrus Sans is outrageously flirting, and to you he just said 'heh, i'm gonna steal that joke'.

The most reliable sign that he likes you, is he would rather be with you than without you. He messages you when he's bored, when he's got a day off he asks if you want to come over and hang out together. He's casually affectionate with you; with everyone else he's very physically guarded, not really allowing any prolonged contact, but he'll sit close enough for your knees to touch and lean on your shoulder. When he's sleepy, he'll just put his head in your lap.

If at any point you're actually starting to suspect that Sans has a crush on you (ie you catch him lightly blushing or looking at your hand like he wants to hold it) that means he's already fully in love with you. If it's obvious enough for you to tell, he's planning to spend the rest of his life with you.

Red: Red is also pretty difficult to tell. Not as hard as Sans, though. He's highly flirtatious in general, but even more so with people he's physically interested in. Sometimes, it can be hard to know if he's just a super flirty guy in general, or if he genuinely really likes you.

When he's in love he switches between totally forgetting to flirt (he's thinking about more than just sleeping together) and acting more like himself, then panicking that you won't like his real self and becoming EXTRA flirtatious and swaggery. He instinctively wants you to see the real him, and like him... but he's also terrified of you not liking the real him, so he clams up and tries to play the part of the big sexy badboy that everyone else seems to like so much more. The longer he likes you the more he eases. If at any point you find out he needs glasses, or that he quit smoking out of fear that it'd impact your lungs, that's a sure sign he's fallen for you.

Another reliable tell is jealousy. Red doesn't get jealous a lot, because usually he doesn't really care all that deeply about his flings. If he shows jealousy about who you're with, it's a big flag that his feelings run a lot deeper than he wants to admit.

Skull: Skull isn't difficult at all. It will be loud & clear that he likes you. Nonstop staring, intense blushing at the slightest interaction, he drops/breaks things a lot because he's distracted just looking at you. His brain -> mouth filter vanishes, he'll be completely silent except to blurt out things like "you're so pretty" and "i like your smell". Before he drums up the courage to start talking to you properly he might even come across as a bit creepy and overwhelming, given his size and strength, the intensity of his feelings, and his love language being staring.

Papyrus usually comes very in handy. He makes Skull seem less intimidating by providing the cute real reasons for Skull's bizarre behaviour around you. He can be a great translation service for his brother- when Skull mumbles something totally unintelligible to you because you make his brain stop working, Papyrus can step in. He's also great at getting that perfect balance between encouraging his brother, and stopping him from crossing any lines; he'll help Skull approach you at a house party without teleporting somewhere completely random out of nervousness, but he'll also dispense helpful advice such as "PERHAPS YOU SHOULD INTRODUCE YOURSELF BEFORE YOU TELL HER YOU WANT TO HAVE KIDS WITH HER."