Two computers to one new one using time machine
(It probably goes without saying, but I haven't actually tried this myself. YMMV. Make backups before you start this. Use at your own risk, etc.)

You probably can, but if there are conflicts between them, one of them will have to be the designated 'winner'.

The easiest way to do this is probably to run /Applications/Utilities/Migration Assistant.app twice. Whichever one you run last will overwrite any of the existing settings from the other one.

A more complicated way to do this would be to use rsync to move the files to the same destination, however it should be noted that rsync is one of the Un*x tools which is hugely powerful and very easy to misuse to disastrous effect. Be sure that you have a separate backup of these files before you try to use rsync on them.

A third option would be to use Transmit which has the ability to move folders and merge them. You'll have to decide which one 'wins' but it’s probably a more granular approach than Migration Assistant without getting into the complexity of rsync.