The OP registered and posted -- got 80 replies and never returned so we don't even know if he read any of this . . .

And interesting that kjaerlighet7 also only ever posted to this thread

Maybe still trying to figure out paragraph breaks

Driving 200kms (124 miles) 2x/week does not prepare you for long haul trips (nor does it prepare the kids!) I do that after work some days!
I used to drive 111 miles every,single.day, and still was not 'ready' for my Texas-Rhode Island (1749 mi) or Texas-South Florida (1200 mi) road trips. And I had a large SUV and only myself and 1 other adult.

If you must visit Texas, I'd say Dallas (FW), Austin and San Antonio. DFW- book depository (JFK shooting), stock yards
Austin- Capitol, 6th street, LBJ ranch
San Antonio- River Walk/Alamo

Don't bother with a car in Boston/NYC/Washington.
You may want a car between these places (Newport RI! Philly- Amish country!) but no need for them IN the city- you'll just be paying a day rate AND a hefty parking fee for no reason.

I too think your hotel budget of $150 for 2 rooms/night is quite high- $75 won't get you much of anything. And NYC/Washington/LA Chicago are big cities, but so are Orlando, Miami, Houston, Dallas, Toronto, Vancouver, San Fran, Portland, Seattle, etc.

When traveling on my road trips, even when staying in smaller towns, you're still looking at $125-$150 for ONE room. And you're not hitting any 'smaller towns'.

I too think you need to remove a lot of stops from your itinerary. I don't know many people who could keep up with this schedule, let alone 4 children who could.

The OP has been back 5 times.

Sorry -- my post should have said the OP never returned after February 14 (I know the OP had been back but we don't know what/if they decided on any of this)

But they have three years to plan so maybe she'll be back . . .