True friends would sit down and talk about it with you, not to judge, not to condemn - but to try to see the difficulties and emotions you are experiencing in having the added stress of dementia to add to the issues of having fertility treatment.
In my humble opinion, this says far more about your 'friends' than it does about you and your husband and your decision. To be honest, my gut reaction is you are better off without them but I can understand that it is difficult if you have been friends for some time and understand how hurtful it must be.
Maybe you can email or write to them to say that this is your decision, made after lots of thought and advice and certainly not made lightly. You would prefer that they respect your decision and support you, but if they feel unable to do so then this will mean that your friendship either cannot continue or only be very superficial at best.
It certainly doesn't excuse their unkind behaviour but do they have fertility issues or reasons why they can't have (further) children? Maybe there is something that you are unaware of but it still doesn't excuse their behaviour.
I join Prudence in wishing you and your husband a successful outcome to your treatment and all good wishes for any and all future additions to your family.
Take care,