I think it’s great you are learning to set boundaries for yourself but boundaries don’t work unless you are willing to stick to them. Your statement of {I “hope”that it will only take a few times, before my husband knows that I am serious about it.} that seems to defeat the whole purpose of setting a boundary.
If you are not serious about it the first time or the second time or the third then what he learns is to dance the dance you are teaching him. You leave he begs forgiveness pleads with you and says anything to get you back home. Then it starts all over again until the next time.
Another suggestion is you may want to re-think telling your parents about all this now. As a parent if my son came to me and said everything is fine today but I may come to you when an un-healthy situation arises for a day or two. My reaction would be if a situation is un healthy enough for him to leave with kids then a day or two is not going to change that situation and I would encourage him NOT to go back. At least not until long range healthy plans are in place for him and any children involved. A day or two does not change un-healthy situations.
Your plan is short term and kind of a long the lines of manipulation to control your husbands drinking.
I am glad you are going to attend al-anon.