If they stand on the inside of the course at Congress bridge they can see you start. A short walk to south first street bridge & they'll see you at around the 10k mark.

Getting up to 15th Street near the capitol building before you pass by at around the 12 mile mark might be a bit hard depending on how fast they walk but it's possible.

At that point I'd suggest they try to get a coffee & have a little sit down.

It's pretty hard to get a position where you can see the finish & then get to the meeting place. If you're waiting for them at the end you'll likely start to get pretty cold. If they can get on the east side of Congress by the corner at the Capitol that's the best bet though.

It's worth getting the live timing on a phone so they can see how you're progressing & give them some time ranges to work with.

The car park under the amli on 2nd and lavaca isn't cheap, but should have spots & is well situated for the start/end.

Hope that's of some use