You will not be disappointed by a 5D IV vs the crop bodies. You would need to get a good lens like the 24-70 II and a flash.
You would be looking at a 4-5 k investment.

Both oh the crop bodies work with your current lenses, so about 1/3 of the money.

For me it comes down to use. What are you trying to accomplish with your images.
Shooting the grandkids I would be ok with the crop bodies. The 7D II is more than adequate. For family it is all about documenting the family moments, seldom is it about creating an image that is art. That type of photography I would be happy with the M5 I bought the wife. I actually shot my stepdaughters weeding with the M5 and it did a very good job (uncle Bob style of course, she had hired a photographer).
if you are a serious landscape shooter the 5D is the better way, if the added cost is worth it to you.