Asked to officiate

Hey everyone just looking for tips, and advice because my friends asked me to officiate their wedding! Here’s some back story for more detail: it doesn’t need to be a legal ceremony because they’re already legally married so I’m not ordained. They wanted someone close to them to do it and make it special. They’re a gay couple, one of them is from Mexico (so if you know of any specific wedding details for Mexican weddings I’d love to know?) they’re both great guys, they have a cat together that’s like their kid now. I’ll be meeting up with them to go over what they want for the ceremony and whatnot but I’d like to come somewhat prepared with my own questions and an idea of how to do this haha. Thanks!!