Sudden desire to become mortgage free !!

[Deleted User]

Im 55. Its never really bothered me to be mortgage free as I receive a pension that will always pay the mortgage. However I was talking to my younger son and he said he would never want the family home to leave our family. I bought it new 20 years ago ( single mum ) and it was designed to my specification. Im now worried and want it paid off - but they could lose it with IHT ? 

Any thoughts ? 

I own three houses
main - value £1 mill - £324k mortgage
2nd - £500k - mortgage £317,000 BTL
3rd - £230k mortgage £155,000 BTL

Im also now worried about IHT as equity as it stands = £ 931k so already to be wacked for IHT ( never be a spouse double) 

I have 19 years on mortgage left - so to 75. I could die earlier so really want it paid off in 10 years - so at 65. 

Mortgage is £1605 at mo 
Im thinking £1400 a month overpayments is what is needed to get it paid off in that time scale. 

I also pay £600 a month to my two sons, so they can pay off their mortgages faster. 

Or maybe I should give them an extra £700 a month each and leave my mortgage higher so providing I live a rolling 7 years a lot of money is taken out of my estate. 

I just dont know ?