I've just been re-looking at some of your other posts to remind myself of your ages and overall position. Depending on the size of your DB pensions, it looks very tight stopping work entirely at this point. The five hours a week would give you a lot more wiggle roomy and, speaking as someone still doing seven hours a week, five years after I supposedly retired, a very good work life balance indeed :)
Choosing when to run down the SIPPs involves a few different factors. I've already mentioned the desirability of getting it out while you have unused PA. Against that there are the issues of possible impact on benefits and the fact that taking anything other than the tax free 25% reduces your annual allowance to £10k pa. If the cashflow works out okay, it may make sense to put 100% of your part time earning into a SIPP, getting more tax relief than you have paid tax. You can even do this whilst drawing money back out of your SIPP if you are still working post 57 - say you earned £8k - which would be tax free - you put £6.4k into the SIPP, government boosts that to £8k and you take it back out for a £1.6k profit and your taxable income is still only £8k!
As regards taking the DB pensions early, I might be tempted to do so when you stop working PT. DBs are great for longevity insurance, but for you the tightest period is most likely to be the period before your SP starts. With the age difference between the two of you, unless there are underlying health conditions, the odds are that you will be the eventual survivor. Have you checked whether any actuarial reduction on his pension would have any impact on the eventual survivor's pension? It doesn't for many schemes.