Confusion amongst the cousins

Definitely cousins. First cousins once removed?

Cousin is a useful word, flexible enough to cover a variety of relationships but still meaningful when used with precision. Case in point: my husband's parents died young so he lived with his aunt and uncle (who were like parents to him) and his cousins (who were like his brothers). So this aunt and uncle served as grandparents for our children, while these particular cousins served as uncles, but then what do we call those cousin/uncles' children and grandchildren, and how do we define the relationship between those descendants and our own children and grandchildren?

Definitely cousins, but what kind?

My son-in-law the engineer knows his cousins as well as his cosines, adept at unraveling all the ins and outs of first and second cousins or first cousins once removed, but those labels aren't particularly helpful in casual conversation: "Hey first-cousin-once-removed! Pass the gravy!"

So I opt for cousin even when it's not quite right. Get all the relatives together and see the resemblances, the repetitions of hair color and facial shape and long, skinny fingers, the common blood showing amongst the cousins, and even the adopted cousins share facial expressions, tones of voice, and baseball teams. Go back far enough and we're all cousins of one sort or another, first or second or many times removed--just don't ask me to do the math!

Not cousins--but aren't we cute?!

Definitely not cousins: uncle/nephew, with complications.