Its better to study article about ternary hetero-structures.

First prepare rGO with suitable functionality that can easily be ligated with Zn and Ti ions. Disperse the functionalized rGO in suitable solvent, add Zn and Ti precursors, then add the base for hydrolysis and polycondensation of the metal ions onto the surface rGO. You may see the following literature for details:

Article Hierarchical Hybrids: Hierarchically CdS Decorated 1D ZnO Na...

Article Synthesis of RGO/TiO2 Hybrid as a High Performance Photoatalyst

Article Synthesis of Graphene-ZnO-Au Nanocomposites for Efficient Ph...

https://www.mdpi.com/2079-4991/8/2/105/htm

Hi Kunal,

The first problem is that rGO is way less reactive than GO, because of losing most of its functional oxygen groups, so you couldn't simply aim for direct bonding between rGO and metal oxides. There are reasonable number of papers that suggested rGO/MO sensors, capacitors or catalysts, which mainly coated the surface of reduced graphene with MO nanoparticles.

Also please consider mixing rGO/ZnO with rGO/TiO2 nanoparticles is not equal to rGO/TiO2/ZnO nanomaterials. Since it seems that you don't mind the nanomorphology of reagents and product, I suggest to search for all possible rGO/ZnO and rGO/TiO2 reactions and try to find the most close reactions to each other (one might be a nanorod with application in batteries and other might be a nanosheet for sensory purposes) and start the reaction with ZnO reagents and after reasonable amount, add TiO2 to the same reaction solution.

For example, let's say you found 2 similar coating methods which use hydrothermal procedure and both used polar solvents and runs in almost same temperature, try the choose the solvent that suits both ZnO and TiO2 precursor, then if it said rGO/ZnO will made after 5 hours, right after 4-5 hours, add TiO2 to the rGO/ZnO and let it run for another 5 hours.