No, there is no obligation to stay at Sandals. Please feel free to stay at another resort or air bnb if that is more suitable for you. However, there will be a Sandals day pass fee of $270 to attend the wedding.
Semi-formal/business casual. Examples of what to wear: cocktail dresses, dressy maxi dresses, dressy jumpsuits, short-sleeved button downs, linen pants, slacks. Suites and gowns are welcome but it may get a little toasty, so use your digression. And please no shorts.
Sandals is an adults only resort, and children are not allowed at the wedding.