My son and I each use TurboTax to file our US taxes from the UK. I buy and download TT and we each use it to file. I file MFJ with my wife, we are both USCs. My son is single and lives close by.
I keep a spreadsheet which I use to record the gross amounts of my UK pensions, interest etc and use the totals January through December. The annual P60s are of little use as they are based on the UK tax year.
I’ve no idea about claiming children, hopefully someone will be along with some info on that.