markmccaughrean, 
You have people at your house for an evening & are eating when the phone rings. It’s your daughter who asks “what’s up?”
Answering:
“We have friends over & we are having fish for dinner”
would be fine, as both parts can be used to describe the present, but:
“We are having friends over & we have fish for dinner”
would be wrong, because both parts sound like they describe the future.
The English language is quite often idiotic 🙄
