Hi, Dina. Tell your hubby to have fun. No sarcastic meaning, just because I've been told, that German is difficult to learn, and I think they are correct. At some point it is better to learn by doing, meaning talking to people or if not possible reading stories.
About the polite form: it is difficult, but to be on the safe side he should just assume to use it with everyone except children. The other person will either respond the same way, then you continue to use it until you both agree to refer to "du" in the future. Or the other person tells you right away that if it is OK with you too they would rather use the familiar form.
It is not only polite to say "Sie" to another person, but it also shows you respect them as either your equal or your superior.
For example children should assume that every grown up is to be called "Sie" except their own parents or relatives.
Very young children mostly don't do that yet, and it is seen as cute, but they learn eventually.
So you say "Sie" to people older than you, and people higher ranking than you.
This is a must.
In this case it is possible to change to the familiar form, but only if the older or higher ranking person tells you so. Never the other way around. This would be presumptuous.
You say "Sie" to people you don't know just to be polite and to give them respect. Including younger people.
Younger people or teenagers:
(Except it it's your friend's child whom you have known since childhood)
Talking to a teenager you say "Sie" at first. Then it depends on the situation.
(more to situations below).
When nut sure:
If the other person introduces themselves with their last name you use the polite form.
If the they introduce with their first name it is safe to say "du".
In thr second case: If you are the one who doesn't want to use the familiar form in this case, it is within your rights to tell the person, thanks but I'd rather use " Sie".
Situations:
# just meeting someone for example in the bus.
You would usually use "Sie" with a person you don't know, especially if it is a chance meeting and you don't intend to meet again on purpose.
# Example: people sharing a hobby and meeting in a group.
Someone would bring it up, like: I would propose that we all say "du" as we will be together for a long time. Does anyone not agree. And if there should be someone not agreeing everyone else would use the polite form for him or her but not to each other. It's about personal preferences that should be respected.
#meeting one of the Weird People in real life.
I would totally consider you to be addressed with the familiar form, not because I don't respect you, but because you feel so familiar by now.
# following example: me meeting Dina's hubby.
Hubby could say "du" to me, even if we don't know each other, because Dina and I are familiar. Of course it would be nice, if he told me who he is first, so I'll not be confused by a strange man jumping up and down from joy of meeting me, lol.
So meeting a friend's partner in life, boyfriend, girlfriend, husband, wife, you would use the familiar form.
...
Oops! This was more text than expected. Sorry for that, lol.
@Dina. If your hubby has any questions, feel free to ask me per private message. I'll try to help, if I can.
I am still learning Spanish. It's almost a year now. Duolingo doesn't do a lot if grammar exercises. I think I will look for a grammar book or something. A small list of regular and irregular verbs and their forms.
And I have a book with children's stories in Spanish on my kindle, because I hope they might be not so difficult to read someday.
