I haven’t done two gallon batches this way (I have a pair of one gallon fermenters), but I have made some two gallon batches with just one gallon equipment (I have two fermenters).
You approach will work, but …
If you are putting the malt/hops from 2 one gallon kits into just 1 gallon of water, you will be boiling a concentrated wort - so you will likely want to adjust the amount of bittering hops.
This thread (“2.5 Gallon Kits?”) may also be of interest. Dividing 5 gallon kits (or recipes) into 3rds makes a lot of sense - but I haven’t given it a try quite yet.
