Is GaP is direcct band-gap material?

Direct band gap means in E-K diagram valance bands are exactly below covalance band,in this band electon fall's c.b to v.b direct without going to metastable state

Silicon is by all means an indirect band gap material.

Yes it is.

Yes it is. Most Sn (tin) materials as semiconductors are direct band gap materials. Silicon on the other hand is an indirect band gap material.

In a direct band gap the electron only needs energy to jump to the conduction band. In an indirect band an electron needs energy and momentum to jump to the conduction band