Having heard of (ακουσαντες). Literary plural unless Timothy is included. Aorist active participle of ακουω of antecedent action to ευχαριστουμεν. Epaphras (verse Colossians 1:8) had told Paul.

Your faith in Jesus Christ (την πιστιν υμων εν Ιησου Χριστω). See Ephesians 1:15 for similar phrase. No article is needed before εν as it is a closely knit phrase and bears the same sense as the objective genitive in Galatians 2:16 (δια πιστεως Χριστου Ιησου, by faith in Christ Jesus).

Which ye have (ην εχετε). Probably genuine (Aleph A C D), though B omits it and others have the article (την). There is a real distinction here between εν (sphere or basis) and εις (direction towards), though they are often identical in idea.