Hi, and thanks for your additional information!
The first and most important thing you have to take care of at this time, is get her spayed. This should mellow out her personality, as she will not be 'hormonal' any longer, and also prevent dangerous health problems from occuring in the future, like pyometra, a serious uterine infection; it might also lower her incidence of mammary cancer.
I would suggest you get a cat appeasing pheromone called Feliway. This product comes in a spray and plug-in diffuser form and helps calm stressed or anxious cats. It's sold in Petsmart and other pet supply stores and for more info, please see:
I think she just has to acclimate to her new environment and may feel uneasy with your dog there (even though he's outside, she still smells his scent, hears him bark, etc.), and if you had previous cats, she surely smells their scents in your home. If she mainly cries at night, as you mentioned, place nightlights in the rooms she frequents most. Cats can't see in complete darkness, as was previously thought. Also, you might leave a radio or TV on low volume to keep her 'company' when everyone is asleep.
Also, if you weren't aware, Siamese are known to be very 'vocal'; they're 'talkers', so this is very characteristic of the breed.
Your son may approach her tentatively, and she senses his unrelaxed demeanor, if he's a little afraid she might strike out, and this makes her more nervous. Or, your youngest son may have a scent on himself, on his clothes, etc., which she interprets as threatening. You can never tell how cats will react to certain smells/people.
I wouldn't 'push' anything at this point. I think it would be best if your son didn't try to pet her until she's more settled in and less nervous. I also strongly recommend the spay surgery ASAP.
After she's spayed and recovered, you and your family can try to play with interactive toys with her, like a laser pointer and feather dancer. Also make sure she has plenty of cat-safe toys to play with on her own, and her food/water dishes and litterbox are in places that are basically quiet and away from the 'traffic' of the household and not near major (noisy) appliances which may freak her out. Also, provide her with a nice, tall scratching post with a 'shelf' on top for sleeping and/or 'surveying' her 'Kingdom' ("Queendom"? lol) below. A kitty condo with many nooks and 'hidey holes' will also help her feel more secure in her surroundings.
Please have her spayed, ASAP and keep me updated on how things are going. I wish you and your human, canine, and feline family much good luck! If, after all is said and done, you feel she is just not a good fit with your family, please contact some no-kill shelters and/or cat rescue organizations in your area and they will pick her up (or ask you to bring her to them) and have her re-homed. Please don't consider having her put down because of her current behavior. It's not her fault.
Please let me know if I can be of further assistance. Thanks!