I can see it's not the first time they've had sex together. It's so convenient - you don't have to take anyone off, there's always a shower and a bed nearby. Of course, her brother's dick is great, so any sister would fall for one and suck it at the first opportunity. Well, it seems to me, he doesn't mind having fun with his sister with it either - his own soulmate won't betray him or make him marry him. It was so cute when her brother came inside her - it just cheered them up. )
When my daughter has naughty conversations with her father, encouraging him in every possible way to fuck her, it is almost impossible to keep within the bounds of propriety. And she promises him pubes like her mother's. So when she took his dick in her mouth, he quickly relented. And soon poured his cum all over her sweet little bud. Cool theme.