Help treating my kids

Well where to start....
My name is Derek and I'm asking for help... I've been with my girlfriend for almost ten years. She was already mom to 3 little ones when we met.. Aaviel who is our oldest now 13.. and Javen and Navaya who are twins now 10.. 4 years ago we were blessed with our first child together Layla.
Melissa stays home bc its a better option than paying child care. I work 2 different jobs but we barely make ends meet... I'm basically asking for help to take my family on a vaction... they deserve so much more than I'm able to do for them. As a father it tears me up inside to tell them "we can't afford that right now"... or when I have to try and make them believe we can get it next week. I want to be able to do something for them since they keep me straight.. they guide me.. I want to do something for them, take them somewhere, make memories that they will never forget.. any help is appreciated and thank u for your time in reading this.