Judging from your last post OP you still don't understand how this works.
All interest only - with repayment mortgages very little capital (rather than interest) is paid off in first 10 years, and as we intend to sell the houses within that time, it makes no sense to have that type of mortgage
Your mortgage is either interest only - in which case you don't repay any capital - you just pay the interest on the capital borrowed or your mortgage is repayment, in which case you repay part of the capital borrowed as well as the interest on the capital borrowed.
What you have described i.e. a mortgage that does repay 'very little capital' in the early years is a repayment mortgage and therefore not an interest only mortgage.
That's good news as at least you will some equity in the properties but it's bad news as the value of the properties will have reduced from the peak price period in which you bought some, so your small amount of equity will be negated by the actual drop in the market value. But - if you hold these longterm you will eventually repay the full amount of capital borrowed. However you need to be able to ride out the inevitable rise in interest rates in the future. So basically you're hoping that when you come to sell, as planned, in about 10 years time that house prices will have recovered to at least permit you to recover the equity you will by then have invested in them.
It's gambling really.
The problem is your timing. Some BTL landlords went down the interest only mortgage route, using each succesive purchase to finance the next purchase. The rents paid the interest only mortgage payments but the real attraction was that house prices were increasing strongly. So essentially, you had a tenant paying your mortgage for you and you could bail out in a few years by selling an asset that had increased its market value substanially.
Unless you can ride out the house price reduction and interest rate increase period you're shafted - but if you can you're minted.
I think your current problem is that you are asset rich but cash poor and that some courageous decsions have to be taken to release some equity now as well as recognising the point at which you may again be over-committed if DH just cannot resist the next attractive deal.