It should be possible to buy life insurance for yourself online. I wouldn't approach your bank, you'll get a really bad deal.
As a first step, you need to look at Martin Lewis's website Moneysavingexpert.com and find his articles on life insurance/assurance. This will help you work out what sort of policy you need.
Your policy needs to give your husband a high enough pay out to pay for full time carers for your disabled children. £1million pay out invested should give him an income of £40-£50k for childcare.
His policy, which as someone else has said, can be provided by his own company, ie his employer, should give you a lump sum to buy a house, or at least a hefty proportion of a house, and a good income from any left over invested at around 4-5% return.
Critical illness cover for you - it can be tricky to choose a policy as there are lots of exclusions. However, if you become too ill to look after your kids, or have surgery that takes months to recover from, then you need enough to pay for childcare.
Your husband needs similar - something that will pay out enough for you all to live on while he recovers.
Again, look at the MSE website, you will find so much help there.
Wills are absolutely essential - they became important when you got married and absolutely essential once you got married. Speak to a lawyer, expect to pay around £1000 for wills for both of you. Make sure you are protected if your husband dies. Nominate guardians for your kids (preferably not your PIL as they don't seem to like kids very much) and executors. The only beneficiaries in the will should be each other and your kids.
Again MSE will give you info on wills so you can learn about them before approaching a solicitor, but you must have them written professionally in your situation.
Re assets: is all the land your DH owns used for farming? Can any be developed into something else commercial? Either residential or business?