The OP has explained above that both ponies have chronic joint problems which are deteriorating and causing significant lameness, i.e. pain, in one pony. You can't draw any conclusions from a happy photo on a sunny day - don't be so quick to judge.
OP - I am really sorry you've had to make this very hard decision, and hope that all goes as well as it can do today. K x
Thinking of you today.
You're a very brave lady and a clearly wonderful mum to your two beautiful ponies.
Take comfort from the fact they were together in life and they'll cross over the bridge together.
An uttery selfless act of kindness. I hope the sun comes out to say goodbye x
My thoughts are with you today. Hope all goes peacefully. Massive hugs to you. They are a beautiful pair and a great credit to you. Remember never a day too early only ever a day too late. You have my greatest admiration and respect for making a very difficult decision. Having been in a similar situation I let my two go together, I didnt regret it. xxxx
They look so beautiful and you can tell how very much you loved them. Very sorry for your loss, you have been selfless in putting their needs before your own emotions. Here's hoping their passing was peaceful. Thinking of you x