When three Jersey City siblings began whipping up seafood in Downtown Jersey City in 2015,their restaurant grew so popular that people would wait two hours for a table, one of them recalled. But the coronavirus struck in 2020, and business was never that good again. Like many restaurants that stuck it out through COVID-19′s months of shuttered indoor dining and the inflation that followed, the restaurant, Just Beclaws, has struggled with fewer customers and higher costs ever since. So with their 10-year lease ending as 2024 arrives, the siblings will be closing the eatery at 280 First St. for …