Adding another node of different hardware and OS and GI and RDBMS

We have a 2 node RAC (machines are 3+ years old)  and want to add 2 new servers to the cluster and delete the old ones. So the cluster will remain a 2 node cluster.

This is what we have now

5.10 Generic_147440-25 sun4v sparc SUNW,T5240

My question is

1. Can we add 2 new nodes of different hardware (more RAM , more CPUs , better clock speed)  to an existing cluster with same O/S ( Solaris 10 ) and same GI / RDBMS version. Its all 11204 for GI and RDBMS.

2. Can we add 2 new nodes of different hardware (more RAM , more CPUs , better clock speed) to an existing cluster with different O/S ( Solaris 11 ) and same GI / RDBMS version. Its all 11204 for GI and RDBMS.