Dear sisters,
I understand the time in which we live it is becoming increasingly difficult to find Christian fellowship with those that want to carry their crosses. When we ladies become convicted to wear modest dresses and headcovering we can become a public spectacle and be mocked openly in public. It can be a very lonely place to walk closely with the Savior and to bear the symbols of submission and reverence in an immodest and irreverent world. What I can recommend to you dear sisters is to make sure you are blessing your husbands. Make sure you are meeting their needs and praying and fasting for them. In the case of the younger sister she can bless and pray for her father.
Next you can pray the Lord's will for your family. Pray for His perfect will as to where you need to be to be in service for Him. I am sorry at this time I do not know of any way to offer a penpal service. But, I can recommend www.charityministries.org for solid Biblical preaching from the Word of God. They also have a fellowship finder for those who do not have fellowship in their local areas.
Another way to possibly find fellowship is through the Keepers at Home magazine. They sometimes have penpal requests in the magazine. They are an Amish and Mennonite publication. You will be blessed by their good articles on godly living and keeping our homes for the Lord.
I want to offer you a blessing that God might fulfill your desires for fellowship. Just keep seeking to be a light in this dark world and may God bless you.