Hi Crocsnap, welcome to the forums.
Really sorry that you and your husband have been through so much these last years. I'm new here too, but I've had a lot of experience dealing with depression on both sides of the coin. First, seeking help is so important and its great that you've made the first step. Your GP sounds pretty on top of things so you will probably get a referral to a good psychiatrist and psychologist for your husband soon.
However, this can be a long and stressful journey and it's important that you set up your own support structure so you can stay well enough to help him and continue to care for your daughter(children?). Consider making an appointment with a psychologist yourself to start- nowadays you can find some who will do online appointments if you feel worried about being away from home more.
I know it's really hard to do, but I think you should consider telling your very closest friends and family about the situation. This will open up more support for you both and they probably already half-know there is a big problem at this point, especially his mother. If you are worried about your husband's reaction, you can ask them to act casual and offer support to you or 'the family' rather than confronting him with their knowledge.
Unfortunately, I think your instinct to hide the medication is totally correct. If your husband is having suicidal thoughts and your GP has suggested hospitalisation, you should keep things like the medication, car keys etc either hidden or with you to remove a source of danger and temptation. There's also the chance that he might throw out the medication if he sees it at the wrong time. I would also seriously consider finding somewhere else for your daughter(children) to stay during this initial crisis period
This is such a challenging and wrenching thing to go through, but you've already done so many things right and your love and supportiveness is so obvious in your words. Remember that you have a lot of support available for you too and don't be afraid to reach out whether here or on a hotline.