[quote=“gmcgough600”]Hi guys
I need to have a conversation with my girlfriend’s parents (not just any conversation, we want to get married this year and I need to ask for their blessing!!). I only recently started to learn Chinese (in the UK where I live with my gf). Here’s something I found online but my gf had a look and said it’s not sincere enough (and she won’t help - says I need to do this by myself 
)
岳父，岳母，我會一生一世對她好，請二老准許我們結婚
Yuèfù, yuèmǔ, wǒ huì yīshēng yīshì duì tā hǎo, qǐng èrlǎo zhǔnxǔ wǒmen jiéhūn
I really want to tell them that I will love her and take very good care of her forever and appreciate the work they did raising such a lovely girl. I also want to promise that we will come to visit them as much as we can.
Thanks for any help with this 
, if someone has any other suggestions of things I could/should say then please let me know…[/quote]
It seems strange to start out by addressing them as “father in law and mother in law” (as you’ve done in your sentence here) before they have given you their blessing. If they are Taiwanese speaking, you could open with “A(1) Bei(4), A(1) Mmh(4)” – “Uncle and Auntie”, often used to address the parents of friends – before continuing with what you want to say in Mandarin. It would be more endearing and seem less like “jumping the gun.” Once you have their blessing, they may just ask you to call them “Mom and Dad”. (I don’t think very many people address their in-laws with the formal terms you used – those are usually used as 3rd person references.)
Better yet, do they understand some English? It seems to me it would be more natural for you to lead into this by using English to explain that you cherish their daughter and ask for her hand, and then throw in this sentence or something like it as a token of effort and willingness to try to make some headway into their culture! In that case, I think the sentence you’ve found is okay, but suggest you replace “她” with your girlfriend’s name in Chinese, and “二老” with simply “你們” (the term 二老 may sound stilted in this day and age, especially coming from a non-native speaker).
Best of luck!