It’s great that you’re helping your parents with their air conditioning installation. When it comes to sizing the system, it’s important not to oversize it, as that can lead to inefficiency and increased costs. A general rule of thumb is that you’ll need about 100 to 130 watts per square meter in well-insulated spaces like your parents' home.

For a 130 m² house, you would typically need a system capable of delivering 13 to 17 kW (depending on the exact configuration and usage).

As for multi-split systems, they are a great choice for homes where you want to control each room's temperature individually. Look for models with inverter technology, as these are more energy-efficient and provide better temperature control.

Some tips:
Brand Recommendations: Daikin, Mitsubishi Electric, and Toshiba are known for their reliability and good customer service. Avoid low-cost or generic brands, as they may not offer the same longevity or efficiency.

Common Mistakes to Avoid: Ensure proper placement of the indoor units (not too high or low), and avoid direct sunlight or heat sources. The outside unit should have enough airflow and be placed in a well-ventilated area.

Good luck with the installation, and feel free to reach out if you have more specific questions!