^^^^^^ This^^^^^
There are those who have posted on the forum about being estranged from children or other family members for various reasons. There is also at least one individual who is long way from where they were brought up and is having to deal with what life is throwing their way, on their own. I am not saying you should be grateful for the cards life has dealt you, but sometimes a peek over the fence at what others have, or don't have sometimes adds a little perspective.
Personally I wouldn't have a problem with child 1 and her husband staying at our house for a couple of weeks, let alone a couple of days and I know she wouldn't if my wife and I stayed at hers for a couple of weeks. - And I suspect I am around the same age and had a similar upbringing, as you. Unless you genuinly think they are going to damage the property, or are incapable of looking after it for you, so what if someone uses a bit more fuel than you would? They are family.