Hi I am so sorry to hear the very hard decision you have to make I feel for you.
As the dad has the son still with him it will not be so much of a shock to lose his partner so I would not worry too much on that side.
If your female is still losing weight despite treatment then you are doing the kindest thing for her.
Sadly I feel some people string it out for the wrong reasons and leave an animal too long before making the right decision and then regret it.
My thoughts are with you xx

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