While every couple is unique, it's generally best to be sensitive and respectful when engaging in conversations with newlyweds.
Here are some questions that are generally considered inappropriate or intrusive to ask:
When are you planning to have children? This question puts pressure on the couple to disclose their family planning decisions, which is a personal matter that they may not wish to discuss. Also, a lot goes into having children, we just don't find them. Mental preparation, financial preparation, and many other preparations are needed to have children. Allow couples to decide for themselves when they're ready without any external pressure. Trust me, they know what to do.
Are you planning to buy a house soon? Financial matters can be private, and it's not appropriate to inquire about someone's immediate plans for major purchases like a house. Why do you even want to know? Planning on helping them financially to get the house?
Did you have a big wedding? How much did it cost? Asking about the cost or scale of their wedding can make the couple feel uncomfortable or put them in an awkward position. Ask yourself why you want to know the answer to this question. If it's to plan yours then ask it in a better way. If it's to just be inquisitive then you don't have a right to ask.
Why didn't you invite certain people to your wedding? Questioning their guest list may create tension and lead to explanations that they may not want to provide.
Have you changed your last name? This question assumes a specific cultural or personal choice regarding name changes and can be seen as intrusive or judgmental.
Are you planning to quit your job or change careers now that you're married? This question assumes that major life decisions are automatically tied to marriage and may touch on sensitive topics such as financial stability or personal aspirations.
Have you talked about having a prenuptial agreement? Asking about legal and financial agreements between the couple is invasive and can be seen as prying into their personal affairs.
Can I come and visit? Even though this doesn't sound harmful, I'd advise you allow the newlyweds to settle into their lives for a couple of months before wanting to visit. A short congratulatory visit agreed by the couple is not a problem at all. Learn to not overstay your visit and not ask unnecessary questions that may make them uncomfortable.
How's the sex going? Unless you're in a position to ask please don't ask. If they're okay with discussing their sex life with you, you're good to go.
Remember, it's always important to respect the boundaries of others and allow newlyweds to share information about their lives as they feel comfortable. If they choose to share certain details, listen attentively and respond with kindness and support.