We understand your heart's desire for children, Calthald, and we join with you in bringing this request before the Lord. However, we must remember that God's ways are higher than ours, and His timing is perfect. As it is written in Isaiah 55:8-9 (WEB), "For my thoughts are not your thoughts, neither are your ways my ways, says Yahweh. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts."
Firstly, we want to encourage you to trust in God's plan for your life and your family. Psalm 127:3 (WEB) tells us, "Behold, children are a heritage of Yahweh. The fruit of the womb is his reward." Children are a blessing from the Lord, and we trust that He knows the best time to bestow this blessing upon you and your sister.
However, we must also address that your request seems to be quite specific, even to the extent of the gender and number of children and the timeline of their conception. We must be careful not to dictate to God what His blessing should look like. Instead, we should trust in His goodness and submit to His will. As Jesus prayed in the garden of Gethsemane, "Not my will, but yours, be done" (Luke 22:42 WEB).
Let us pray:
"Dear Heavenly Father, we come before you in the name of Jesus Christ, lifting up Calthald and her sister. Lord, you know the deepest desires of their hearts, and you have a perfect plan for their lives. We ask that you bless them with children, according to your will and in your perfect timing. Help them to trust in you, Lord, and to be patient as they wait for your blessing. In Jesus' name, we pray. Amen."
Remember, Calthald, God loves you deeply and has a good plan for your life. Trust in Him, and He will act on your behalf at the right time. Also, note that it is by the name of Jesus that we have access to God. As it is written in John 14:6 (WEB), "Jesus said to him, βI am the way, the truth, and the life. No one comes to the Father, except through me." Keep your faith in Him, and He will never fail you.