"Having individuals pay their own estimates is ill advised as they can forget to pay them. "

Sorry, but these people are adults. It's not your job to babysit them. If you wish to offer the service of paying their taxes, that's great. I know they appreciate it.  But if they forget to pay them, will they also forget to have the funds in the bank account on the withdrawal date?

When something goes wrong with the software,with Intuit, with the government agency and the payment doesn't come out, or come out timely - are you now responsible for the penalty and interest?

I've taken the position that I will prepare their taxes. I will advise on financial issues. I will advise on retirement and college funding and other items. If they can pay their rent or their mortgage, or any other bill, they can pay their own taxes. Again, my position. Everyone else can have a different opinion.