Sister's birthday party will have big of drinkers and a lot of alcohol.
My husband will be out of rehab for only 2 weeks and I'm working on my sobriety.
My Father thinks we should show up for a little bit anyway, but both my husband and my social anxiety will be off the charts. Do I go or do I politely bow our? And what should I say to family?
If you have a sponsor or someone you could call if you get uncomfortable, than I’d go for a little bit. Show up maybe a little early before the drinking gets out of hand and politely leave if you get uncomfortable!
Remember: you do NOT need to go anywhere you don’t want to. If you do: be prepared. Bring your own kombucha or alcohol free treats and have a clear exit strategy. Your health is more important than your sister’s birthday.
Show up early. Your sister should understand and respect you. Share a hug and leave. Keep your sponsor and support group on speed dial.
Thanks everyone! Showing up early before everyone gets too loaded, is a great idea! We'll eat and leave.
Showing early is a great idea! Thank you. 
Bringing special drinks and treats is a great idea too! Thank you!
If the anxiety gets too out of control, I won't go. It's not worth it for it to go bad. Thank you!
If you're comfortable, tell your sister that you and your husband are willing to attend her party for the first hour or two if she doesn't permit alcohol during that time.
I agree with everyone else's suggestions, too. Just throwing out another.
It's a surprise party, so.. Anyway, I think an hour or two will be good! Thanks Amanda!
You have to do whats best for YOU! You do not owe anyone an explanation for your time! If your sister loves you (im assuming she does ◡̈ ), then she
should completely understand and support you! Show up for a couple hours if you feel comfortable! If you dont take her out to dinner or do do something special the two of you!
It sounds like your husband and you are making some pretty great changes to better yourself and its still in the very early stages! Do what is best for you and the people that love you will understand and support you along the way!! 
Try to politely bow out, and if that don't work just be blunt. Tell them you would love to be there to support your sister, but the risk is to great so you won't be there. Your health is just as important as her feeling you love her.
If all else fails, it's a great idea to do something separate from the event with my sister! The alcohol runs thick in my family, so some are not so understanding but that is their issue. Yes, some huge life chances! We've been drinking for 3 decades and that is NOT living! Thanks Kristi!
You got this!! 
Oh...yeah, don't ruin the surprise. 
I'm still deciding, Steven. My husband isn't even out of the 5 week inpatient. I should probably see if he is strong enough. You're right, it's not worth losing our sobriety over! Thank you!
Both you and husband write a nice birthday card wishing ur sister the best ! Tell her both of you will attend next years birthday party !
Rory, I'm already rethinking it! Thanks for your support.