TSO 129 GPS receivers can not be used to satisfy alternate requirements, even if you have 2.
...
TSO 129 + NDB or VOR = alternate req
On further investigation of the AIP, TSO129 receivers can be used to satisfy alternate requirements, provided there is a ground-based approach at the aerodrome and alternate if required, so in this case quoted, you would be OK.
(AIP Gen 1.5 para 8.5.5.3)