It looks like you're on the right track with your answers, but there is a small error in each of them. Let me help you correct them:
1. Carmen y Sofía / mostrar / las fotos / a Milena
Your answer: Carmen y Sofía le muestran las fotos.
Correction: Carmen y Sofía le muestran las fotos a Milena.
Explanation: When using the indirect object pronoun "le," it is important to clarify to whom or to what the action is directed. In this case, "a Milena" specifies that the photos are being shown to Milena.
2. nosotros / vender / ropa / a los clientes
Your answer: nosotros les vendemos ropa.
Correction: nosotros les vendemos la ropa.
Explanation: The mistake here is missing the definite article "la" before "ropa." When referring to a specific item, such as "la ropa" (the clothes), we need to include the definite article.
3. Javier / prestar / el abrigo / a Gabriel
Your answer: Javier le presta el abrigo.
Correction: Javier le presta el abrigo a Gabriel.
Explanation: Similar to the first sentence, it is essential to specify who is receiving the action. In this case, "a Gabriel" indicates that the coat is being lent to Gabriel.
Overall, your understanding of using indirect object pronouns and the present tense of the verbs is close. Just remember to make sure you include the necessary clarifications and definite articles when forming your sentences. Keep up the great work!