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You definitely want to honor the whole family this way, not just one individual? So given names are out of the running?
McCarty wasn’t who your grandfather was-- he was adopted by his stepfather, if I’m reading you right. If the name has a chequered past it doesn’t sound like you want to honor them anyway.
If you like the Cauleys, I would use Cauley, full stop. Perhaps they were McAuleys back in the day, but the people you know of and wish to obtain continuity with were Cauleys.
It doesn’t sound too wonderful as a first name, but has a great rhythm and pairs beautifully with most classic boys’ names.
I like the idea of combining the two names into [name]Macauley[/name]. If it’s meaningful to you, I wouldn’t worry about any famous references. Most kids won’t know who Culkin is anyway.
Cauley as a middle seems very usable to me. I wouldn’t combine them.