Lyla is so pretty and romantic, I think you could get away with a longer romantic-style name for a middle name:

Lyla Alessandra
Lyla Isabella
Lyla Katerina
Lyla Evangelina
Lyla Esmeralda
Lyla Cassandra
Lyla Cordelia
Lyla Evelyn (had to put something that didn't end in -a! My cousin's name is Evelyn)

I would stay away from two-syllable middle names if her first and last name are also two syllable. But I love the choice of Lyla, so pretty

For Angus, I like Angus Benjamin. Some other choices:

Angus Jacob (breaking my no-two-syllable-middle-name rule I know, but I love it! And AJ is a cute nickname if you wanted that)
Angus Gabriel
Angus Nathaniel
Angus Seth
Angus Chase

Hope you find something you like