Salaam Sr.
I read your post and I guess I could relate to what you said. I have been in this siutation before. If anything, I do not think your friends will look down on you, they respect the way you are. However, it does seem different to them, so you may get a bad vibe from them (that is how you feel from them).
If you are going to teach them religion, simply be yourself. That is dawah in it own form. If you are going to say anything or teach them, keep it simple. Talk about it in your life experience and you carry it on a daily basis (e.g. saying how praying gives you self-assurance and that you feel like everything is going to be okay.) This may reflect on them.
If you are going to say anything to them, keep it at a minimal. Religion is a sensative issue with anyone and everyone, and we all take it in at different levels. (e.g. saying how praying and preaching on lay-ul-tal qadr washes away your sins from the past year) Something like that. You want to be easy with it. If you go at them and preach all the time, they may not take it lightly and it becomes personal.
For people to take religion seriously, it takes some people time or it can happen overnight, it all depends. Nonetheless you have to be patient with them or anyone, and simply pray for their sake iA.
I would also recommend to invite your Muslim friend to events perhaps. If there is a sister's halaqa for instance, be kind and tell her about it. If she goes, then she goes. However do not pressure her. From time to time, try to keep her eyes open for such opportunities.
As far as spending time with these friends, I think you should just be straight-foward and tell them. If they want to go to a place that may lead to fitna or sin, do not hide it from them. I would suggest that you all can hang out another time, and do something simple such as getting lunch at a joint or grabbing some coffee where you all can chat. It still shows that you want to spend time with them.
Of course I cannot tell you or anyone to be friends with only certain people. However, when it comes down to Islam vs. Friends, Islam is what matters in the end. Anything and everything you do is for the sake of your religion. It seems like you want to take religion seriously, so if these friends respect it or do not, then that is their motive. You have your own program. If you want to strengthen your deen, I think it is best to maybe hang out with more Muslims and it's community.
I have always been told that if you want to make it to heaven, you want to associate yourself with people who can help you get there and influence you in that manner.
FINAL WORDS OF ADVICE, IN A NUTSHELL:
Insha'Allah continue to be yourself, work for the sake of Islam, and do not let anyone stop you from doing what you do. Ultimately, I am trying to say is take your religion seriously, and this is what matters the most. If you think these friends will hold you back, then let go of them. If you feel like you cannot influence them, simply make an effort to move on. You are on a roll and do not look back. Also try to make more Muslim friends and be active in the Muslim community.
Allah bless you insha'Allah.