“…where α > β > 0, ω, τ are constants and D t α , D t β are Riemann-Liouville fractional derivatives. In practice, the study of the qualitative properties of solutions for the corresponding fractional models such as existence, uniqueness, multiplicity, and stability is necessary to analyze and control the model under consideration [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In [3], Zhang xðsÞdAðsÞ is denoted by a Riemann-Stieltjes integral and 0 < β ≤ 1 < α ≤ 2, α − β > 1, A is a function of bounded variation and dA can be a signed measure; the nonlinearity f ðt, x, yÞ may be singular at both t = 0, 1 and x = y = 0.…”