I think the SIL's saying "hope you can make it" says everything we need to know about the dynamics here: 'Hope you can make it" speaks to the invite being one of those "We've rented a place big enough to accommodate everyone. If you can make it. great! If not, then we will miss you but understand. It is a casual invite. You made it clear you don't want to be around "any of those people" so sounds like you have made no effort to be part of an extended family and that often happens when a person wants supreme control. To view an invite to a villa, paid for by family members, as controlling can only be viewed as such by a controlling person themselves. Those of us who are not control freaking our lives would see this invite as lovely and generous, whether or not we wanted to go. Your not liking to be around the other side of the family and seeing this as controlling speaks volumes about you unless of course they are all hatchet murders.
There is no expectations or pressure except what you are trying to make it out to be, which in turn puts pressure on your DH. I have heard exactly zero about whether DH or children want to go. Kids often enjoy being around cousins, etc. on holiday- relieves some of the boredom of just hanging out with adults or each other, especially if they bicker or are competitive. Not saying yours are but just saying such holidays can be great fun for other sin the family who too have opinions, wants, needs, desires.
Also, if you typically go through DH for everything MIL concerned because you have such negativity towards your MIL and don't want to communicate directly with her or have implied that, then don't be surprised when MIL doesn't ring you to tell you the plans she made, which she has a right to make. Perhaps your DH, if he wasn't being manipulated by you to conform to your needs for supreme control over his life so you can have your needs met, has an opinion and might want to go but is afraid to express that for fear of your wrath and dealing with the moodiness his non conformity to meeting your needs brings on ? Perhaps the children would enjoy the trip? All I hear is "I want, but I want...." "Hey, what about me?". I hear anger, great dislike and creation of drama where there should be none. Everything going through SIL? Is that because you have made it horrifically uncomfortable for DH to communicate with family through pouting, withholding affection, etc. You see, family members, including extended, will slowly learn they have to be very careful around an in law who doesn't like to be around them in order to manage being with a sibling or son they do want to see but who is becoming increasingly unavailable for a relationship due to a partner's behavior.
Your MIL has every right to rent a villa and invite whomever she wants, including you and your DH and her grandchildren. You have the right to decline if you make that choice as a family and not bully your husband or your children. Your husband has a right to go and you have a right to stay home and cheerfully see them all off if it is an experience they want to have and then enjoy some serious 'me' time since 'it is all about me time" that seems to be what you prefer anyway. I think you are reading far too much into this or you failed to give enough background to support accusations of manipulation.
Sounds like a nice gesture and severe overreaction on your part that you are trying to garner support from from other's who need to control every aspect of their partners life, a form of domestic violence.