SOs family! Long rant!!!

I don't know what to do with these people anymore! I cut hair for a living, that's my career and his family contatntly wants me to cut or color their hairs specially his mom and sister. I don't charge them much because of course it's his family and I try to also help them out, they are EXTREMELY sensitive they literally get butt hurt over anything. Anyway today his sister called me asking if I could go cut her hair and her mom's so I said yes, she asked how much it would be I said $5 each and she said OK. Then she texts me to tell me neither of them have money they'll pay me later, I told her I needed that money for the gas at least and she said OK I'll see if I can get the money by the time you get here I said fine and then I get here and still neither of them have money and I'm about ready to cut their hair last time I told them I needed them to pay me they literally didn't talk to me for about a month I told my so and of course he was mad at them for not paying me and told them crap. I'm not a mean person I can't find it in me to say no when they ask me to do something even if they 'pay me later' which they never do. Like what can I do or how can i become stronger lol to tell them no if they don't have the money in hand??