I've no real experience of putting up antennas on the chimney of a house.

Obviously, I must not overload the chimney breast.

I think your antenna plan is workable.

At one qth I had up a 2 element 10m yagi and a 5 el 2m yagi on a chimney
mount. Replaced those with a 2 el 15/10 quad for a while.

This was with a Radio Shack chimney mount. Just the chimney mount by
itself was too flimsy. I found that it was necessary to add a set of
guys, attached just below the rotator and running to the roof
corners. The guys made the whole thing much more secure and took some
of the windload off of the chimney.

Torsten
N4OGW