I still can’t see what the problem is, other than estate agents wanting an easy life. Lived in homes, if they are kept clean and tidy usually present better than empty ones. Agents normally hate having to deal with tenants, but this is not the case if tenants are supportive. .
So. Speak to your tenants and ask if they are interested in buying. Offer them a price which is at the lowing end of what you would accept minus agents fees. You are better off as you have rent through to the end, motivated buyers and no hassle.
If not ask if it is ok to market with them in situ. Then be very clear to agents. You want to keep tenants on side, so viewings only to qualified and interested buyers only, and respectful of tenants wishes. Explain that a BTL buyer would be ideal.
I can’t see why a BTL buyer would expect a discount. Starting with good tenants in place is perfect. And the legal stuff is not complicated. And if the buyer wants vacant possession, you get this before exchange...giving a bonus to the tenants if they have been helpful.
DH bought his first house as a tenant. It was brilliant as the landlord let him keep all the furniture etc so there were no initial move or furnishings costs. And the landlord did not have the hassle of disposing of stuff. DH was also able to keep his flat mates, receiving rent from them.