Moving to Pittsburgh from Houston with 5 kids!
Pittsburgh is NOT pricey like cities closer to the coast. Real estate and everyday items like groceries are priced similarly to the Midwest.
I live in Squirrel Hill and love it, but with 5 kids you might find it more economical to drive than use public transit, and the traffic and parking are somewhat difficult in Squirrel Hill. City neighborhoods that are a little less dense, but still close to everything and with plenty of big houses, include Highland Park, Point Breeze, and Regent Square. The city public schools are a mixed bag; some are very good, and there are magnet schools. Just south of the city, Dormont is a nice place with decent public schools; Mount Lebanon has very good schools but is higher priced.
There is a mosque in Oakland, a city neighborhood that's a short drive (and very accessible by transit) from any of the neighborhoods I mentioned. I've been to non-religious meetings there, and the members seemed very friendly. I believe there's also a mosque in the eastern suburbs, maybe Monroeville?