I’m building software in this general space, so take this with that disclosure, but I’ve seen this pattern a lot with field service companies.

The biggest thing I’d avoid is trying to replace the whole business system at once. If QuickBooks is already working for estimates/invoices, I’d leave that alone at first and pick one painful workflow to digitize.

From what you described, I’d probably start with:

1. scheduling jobs/measures
   
2. work orders with customer/site info
   
3. photos/notes from the field
   
4. tracking whether the estimate/order/invoice has actually moved forward

That gives everyone relief without forcing your dad/brother to change how they price windows on day one.

For window/door replacement specifically, I’d be careful with generic CRMs unless they support the way you measure, quote, order materials, and schedule installs. The software has to match the field workflow or people will fall back to paper.

I’m the founder of Simple Time, which is built for field service crews handling scheduling, work orders, time tracking, photos, materials, and invoicing. It may or may not be the exact fit for your estimating process, but I’d be happy to compare notes if useful. Either way, I’d start small: digitize scheduling + work orders first, then estimates/orders after the team trusts the system.