Mandatory Date night.
We had date night weekly before our daughter was born 17.5 yrs ago and we still do. The only time we missed was if someone was sick.
Yes, it cost us some bucks for a bunch of years but we strongly feel it was a priority to our relationship. I routinely paid $60-$80 a week for a sitter and now my daughter gets paid to sit for neighbors who have the same priority.
Things to do...
You don't have to do anything fancy that costs a lot of money. You can just walk through nice shopping centers, parks, etc.
We love great restaurants so we do that about once a month.
We belong to a nice country club and we are there weekly... sometimes just for cocktails and sometimes I ride the cart and watch hubby practice.
We have Top Golf here that is a load of fun
It is not a matter for us finding time... it is priority to make the time.
Your children are in a wide age range... you have a couple of children who should be able to babysit (and be paid a reasonable fee) your younger children.
GO make it happen....