Which statements are true for compatible goods or goods using the same standard?

This is exactly the definition of complements which are defined by a negative cross-price elasticity (price for a good increases leads to less demand for the complementary good).

This is true. To align the standards of complementary products much effort and coordination is needed. For example the standardization process of cell phone chargers and different cell phones is very hard to achieve because most suppliers have their different systems (adapters…).