Is there membership for a house church?
Membership in a house church is not the same as membership in an institutional church. In an institutional church, the government has specific requirements of members in order for the church to maintain it's non-profit status. In a house church, the only reason there would be membership is if the elders want the people to agree on doctrine and core values.
Can I be a member of a house church and an institutional church?
Although this is theoretically possible, it doesn't make sense practically. The reason for being a part of a church is to be involved in a deep and intimate way. Every house church member should look to spend as much time as possible with each other.