Don't Want Another Episode of Shame

Good evening ma'am, please, I need your advice/help and that of your fans urgently...
We are four in my family(2 boys, 2 girls)...
My elder ones( the first and second born- all boys) brought disgrace/shame to my family when they were teenagers.
The first born impregnated a girl, not up to three years the second born impregnated a girl again despite all the advice and teachings from our beloved mum(she's a widow), the shame was so unbearable for this poor widow...
Now, my kid sister(16years) who just graduated from secondary school want to start misbehaving.
My church pastor who is around 29 years came to seek for my little sister's hands in marriage and we advised her to dedicate her time in serving God and face her career, it is not yet time for her to start thinking about marriage-
If it is God's will at the appointed time he will bring him not now and she's yet to know her left from her right, she can't make sound decision at this age..
We advised her not think about marriage now, she should at least have a certificate from a higher institution first( we are all graduates in my house, she's the only one seeking for admission) and she told us that she loves the man( can you imagine) but we warned her never to go to his house.
I got the surprise of my life this evening when I picked her phone with the intention of browsing sum information regarding her POST UTME and I was tempted to go through her facebook chat with our pastor...
I couldn't believe my eyes, a girl of 16 years  calling our pastor sweet heart, my love and talking nonsense...
What shocked me most was that my little sister even had the gut to visit our pastor in his house( he stays alone) and told him not to let anybody know about it..
I don't really know how to go about this, i don't want another episode of shame in our house......
This pastor wants to cause problem in my family because he is really confusing my little sister...
Sorry for the long write up. Thanks and God bless y'all.

I understand how you feel about the attitude and the yearning of your younger sister. 
I know that you have good intentions for desiring to see her discover her purpose in life, avoid some mistakes that may cost her of her happiness and fulfilment in life. 
I commend you for your sincerity and compassion for your sister. 
I feel that what you need to understand at the moment is that your sister just as well as every other teenagers is struggling with the their new identity and the new personality that their hormones is forcing on them. 
She suddenly discovered that her boobs is beautiful and her vagina has some fluids. 
She ovulates and young boys in her area compliment her every now and then. 
Your pastor for the reasons best known to him has found her innocence and naivety attractive and has decided to explore that to his favor whether positive or otherwise. 
What your sister needs now is no longer instructions, commandments and warnings because she yearn to discover the world by with her own rules and laws. 
She feels accomplished knowing that she could fall in love just like you and that she could have her own man (whatever that means to her). 
What you need to do is bring her closer to you and find out more about her vision and plans for her future. 
Ask her about her boyfriend and their plans, be liberal but mindful of your purpose for bringing her close. 
Feel free to ask her how she hope to raise children at her age, how she can make money and survive the challenges and turbulence of life. 
Listening to her express herself will help you strstegise how best to reach out to her understanding. 
In our present time, it is difficult to track individuals with the advent of social media and you can't help but accept the fact that your sister need your love much more now. 
Bringing her close to you will help you to influence her positively and limit her from communicating with her boyfriend. 
You may also take her to the hospital so that she will have some time with teenagers who got pregnant and possibly learn from them, and also learn more about sexually transmitted diseases and infections. 
While you expose her to all form of information that will help her make healthy decision, please don't hesitate to pray for her and take her to programmes that will change her perception of life and her desires in life. 
Do not give up on your sister even though her attitude maybe somewhat frustrating, it's not unconnected with her passion to conquer the world and enjoy the best in life all as a result of her hormones. 
You may also read this I'm Heartbroken and gain more insight on how to help your sister overcome this phase of her journey.